Sculpting - ****
As a Lego product, there are really two ways to consider this category. First, there's how well the toy evokes the source material as built according to the instructions. Second, there's how much the toy makes use of the Lego concept, how works as a "construction" toy.

As far as the first approach is concerned, this set nails it. Personally, I think the Star Wars sets have been hit-or-miss. The Cloud City set was a jumbled mess that didn't really look like anything from Empire, and I'm not sure how I feel about the upcoming Home One ("It's a
trap!") ship. But the Death Star here looks EXACTLY right. Each room is a mini-playset in itself, the look is 100% accurate, and even small details are there. The cameras in the detention block, for example, look exactly right, as does the Emperor's throne room and the "flower petal" terminal consoles. The railing where Luke batters the fallen Vader until he lops off Vader's hand? It's there. The little black half-globe at the center of the conference room table? It's there. The white arrows on the floor of the hangar? They're there. The angled black walls and distinctive grated floor of the detention block? All there. The strange conical things hanging from the ceiling in the chasm area Luke swings across, the shape of the blast doors... it's all there, all perfect. Oh, and just like in the previous "Death Star II" set, there are transparent greenish-yellow pieces which plug into the dish so the Death Star can be "at rest" or in full firing mode. Cooool.

This set, more than any other Lego SW set, really feels like they went out of their way not just to evoke Star Wars, but to reproduce the minute details of the Death Star. Plus, just in terms of "what areas should be included in a Death Star playset" issues -- There isn't much that takes place on the Death Star that this set leaves out. We've got, from top to bottom, the Imperial Conference Room, the Superlaser Control Room (where Leia watches her planet die), the tower cannons shown during the final attack, the detention block and Leia's cell, the Superlaser itself, the Emperor's Throne Room, the chasm Luke and Leia swing across, the "red room" where the heroes first arrive and R2 discovers that Leia is scheduled to be terminated, the hangar where the Falcon is kept, the blast doors where Kenobi merges with the Force, the giant cannon shown during the final attack, the garbage compactor, the tractor beam console. Really, all that's missing is the trench.

There are a few places where I could quibble about placement (the elevator corridor where our heroes first escort Chewbacca is on the bottom floor, so there isn't a proper chasm; the tractor beam is on the next-to-bottom floor, while it feels like it should be at the top; the window behind the emperor's throne overlooks the TIE hangar rather than space itself) and size (the "red room" is tiny, just a small platform in the superlaser area). But there are just as many places where the orientation is perfect: the red room windows overlook the hangar, so stormtroopers can let their commanders know about bad transmitters, and the blast doors where Kenobi and Vader duel are located right at the hangar as well, and of course the detention block is right over the garbage compactor.

And all that just covers what's in the movie. They've also included a droid factory which also passes for a torture chamber, a maintenance area complete with a crane, and a space at the bottom which is just open area ready to be filled with whatever you want. Somehow, a set that includes just about every Death Star area shown in the movies also finds room for some creative Lego suggestions of the stuff they DIDN'T show us. (Incidentally, I've called the Superlaser itself an area we see in the movie, since we do, and there is something like that here -- but it's not really movie accurate. The consoles where the gunners sit aren't here, nor is the tunnel where we see the laser. Instead we have a massive console and sci-fi-lookin' STUFF that moves around, behind the big dish. It serves as a neat "suggestion" of what we saw in the movie, but it's the only time Lego substituted its own version rather than go for accuracy. I suppose the "red room" area could double as the tunnel where the laser shoots past, but it really doesn't look like it, and it DOES look like the console where R2 finds Leia's cell and the tractor beam terminals and Luke convinces Han to mount a rescue mission)

As for thinking about this set as a construction set and not a ready-made playset....

Well, the sheer number of bricks makes this a great set for just about any builder. No brick is in itself very Star Wars specific, so I wouldn't say you could use this as a basic set to create any Star Wars environment.... but this set could be tweaked pretty easily, and by building on the ways the instructions do things, you could probably make sections from a Star Destroyer, or other portions of the Death Star not shown here (if you can think of any!) There are enough open areas, too, where with other Lego bricks you could add your own details, or rearrange things in ways you prefer. I, for example, am not crazy about Vader's TIE fighter, so I pulled out my old mini-shuttle from a few years ago. It perfectly fits into the hangar, and looks GREAT there. Sure, it's out of scale, but I don't care. I love it. And I prefer an open area to the crane, so I can display ranks of stormtroopers. It's not even "customizing," it's the play pattern Lego was made to encourage. There's a lot more one could do if so inclined.

Having said that, though, there is one respect in which the design of this set was EXTREMELY frustrating to me. Usually, Lego allocates bricks in large sets like this in numbered bags, which the instructions indicate to open in a particular order. When working on one portion of a model, one only opens the bags containing the pieces one needs. Not here. This, by far the largest Lego set I've ever owned, contains four large boxes, coded with symbols to which the instruction booklet does not refer, each containing many celophane bags, all of which must be opened at once. The box is roughly the same size as the BMF or the AT-TE box - and IT'S FILLED WITH TINY LEGO BRICKS. In no particular arrangement. Good luck finding that piece you need! Probably by about p. 
75 of the 260 page instruction book, I'd needed to open most of the bags. Pieces are not entirely randomly scattered throughout the bags, but neither are elements for one particular area confined to a single bag or set of bags. Again, there's a large quantity of bags, and you very quickly are required to have all of them opened, which means any given piece could be just about anywhere. I'd often spend twenty minutes hunting for the right piece, and I have to admit, much of the time I found building this thing to be annoying. If I had more space to lay out and organize the elements, if I enjoyed jigsaw puzzles more, if I had more time, maybe it would have been different.

In the same vein, I noticed that this set doesn't share a key element with some other big-ticket Lego items, like the Green Grocer, Market Street, and Cafe Corner sets. Those sets also contain multiple floors, only the floors attach to the lower levels only with a few strategically placed pegs. They are readily removeable, to allow greater access to the interior (not to mention, easier to move, and to store if you'd rather not disassemble them in their entirety). The Death Star doesn't do this. 

I think it would have been a great idea to make it easier to separate at least the top half -- which would be theoretically possible, inasmuch as there are no key shared elements which would undermine structural integrity if you gave it a shot. As it is, the final set is HEAVY to move, and a bit nerve wracking -- it's a sphere, so the "base" is actually much smaller than the widest point of the model, which doesn't inspire confidence as you move it.

That said, these are minor complaints about the finished product.

A few other things. First, again, this set is HUGE. Most rooms are big enough to accommodate serious play, as though they were each playsets unto themselves. The detention block, the superlaser, the throne room. Others are smaller, like the tractor beam area or the red room, but still and all, between what's included and how much room most areas are given, the sum total ends up being overwhelming. It doesn't convey the massiveness of this thing to see its dimensions written out. It's a sphere, remember, so even if it's only a few inches taller than a regular 12" figure, it's got way more volume. Even if you have shelves that can accommodate its height, it seems unlikely you can accommodate its depth. This thing needs a pedastal, or more likely a coffee table, to be displayed. This thing dominates any space it occupies.

Second, I want to comment on the choice to make this an open sphere. I've never been crazy about the notion that a Death Star playset has to somehow resemble the Death Star from the outside. The original DS playset, and the Micro version that came out in 82, neither sat in a sphere or circle shape, and both were amazing. Galoob twice tried to do a Death Star that looked round, once in Micro Machines and once with Action Fleet. Both sets wanted to make a Death Star that looked right from the outside without caring as much about what went on inside. It was a mistake, I think. This set, happily, nails it. There is no way to give this set is exterior "wrapping" (short of imaginative use of Lego pieces - never say "there's no way" when talking about Lego, after all) so it won't really serve as a good model of the Death Star seen from space. But you don't want a hastily cobbled lump of rooms, which is partly what killed the Lego Cloud City set. So what do you do? Putting everthing together as a doll's house, but making sure it fits in a sphere, is probably the best solution. This way, it looks like a cutaway or X-ray version of the station, and it doesn't feel like Lego was thinking "how can we fit this into a sphere?" but rather "what shape should these sets all form when done?" Really impressive that Lego pulled this off.

Paint - ****
I was tempted to just leave this category as "N/A" but then I realized there is SOMETHING to be said about it. There are two kinds of decos in this set: decals painted right on the brick, and stickers you have to apply. There are only a few of the old-fashioned decal bricks, all of which are computer terminal pieces. The stickers, though, serve as Star Wars-specific details, like the unique light configuration on some of the hangar walls, and the unique elevator display. One serves as the backdrop for the detention block corridor in which our heroes find themselves trapped. And the control room screen can show either Yavin IV coming into range, or Alderaan floating peacefully in space. Perfect details to capture the right look. I love the stickers. The set is already amazing, and would be fine without them, but they really take it that extra mile and give the set a very distinctive Star Wars look. They turn what might have been "Oh, I can see how that's kinda the Death Star" into "Hey, a Death Star playset." 

Features - ****
This is going to take a while. Make yourself comfortable. I'll begin with the movie-accurate features, those which capture some moment of the film as opposed to those which are just creative Lego inspiration. At the top we have lever-operated tower cannons (which move in sync) with guns which raise and lower with the turn of a knob, we've got the viewscreen with swap-able Alderaan or Yavin displays, we've got a terminal which remotely moves the Superlaser dish. At the next floor we have a moveable TIE fighter rack which holds Vader's TIE (complete with opening cockpit), a mini-elevator which brings troopers to the hangar, a collapsible catwalk in the Emperor's throne room, the Emperor's throne itself swivels, there's an opening door to Leia's cell, an opening grating in the detention block corridor with a drop to the garbage compactor below, a moveable camera in the detention block control room, a chasm with a rope for Luke and Leia to swing across, and a blast door which can be remotely shut and opened with a knob. At the next floor we have garbage compactor walls which remotely close or open at the push of a lever, an escape hatch from the compactor which slides open, the column of light over the tractor beam which shuts "off" when a lever is pulled, and a rotating cannon which firing missile. And running through the center of it all, an elevator which goes to each floor.

As for stuff we never saw in the film, there's also a raisable rack in the droid factory/torture chamber,a hidden armory in the conference room, a moveable crane in the maintenance area, and even the chairs at the conference room all swivel.

Accessories - ****
Tough to decide how to prescibe this category. What is a feature, and what is an accessory? I'm going to include all non-fixed pieces as accessories -- seems as good an approach as any (though then I'd also technically have to include the bits and bobs they've included as "garbage" for the compactor, which it feels wrong to include, so...) Consequently, I'll say this set includes Vader's TIE fighter, three lightsabers (blue, green, and red), many many guns (pistols and also rifles), force pikes for the Imperial Guards, removeable helmets of course, and the following figures (get ready, it's quite a list): Luke Skywalker, Luke Skywalker in stormtrooper disguise, Luke Skywalker as Jedi, Han Solo, Han Solo in stormtrooper disguise, Leia Organa, Chewbacca, Ben Kenobi, R2-D2, C-3PO, Emperor Palpatine, Moff Tarkin, Darth Vader, two royal guards, two stormtroopers, two Death Star troopers, an evil 3PO, an evil astromech, an "assassin droid" (a white IG-88), an interrogation droid, a mouse droid, and a dianoga monster. 

Whew! Part of what makes this set so tempting is that it not only gives you every Death Star location you can imagine, it also gives you just about every ANH figure you could want, plus an Emperor, Jedi Luke, and royal guards to boot. We get all the basic heroes, we get stormtroopers, DS troopers, Vader. There's no way to explain having figures from ESB here, and a rebel pilot in X-Wing gear would be a stretch. I suppose Death Star gunners would be nice (given the presence of, well, a Death Star gun, not to mention the Superlaser itself), and I'd love some TIE pilots, even without the TIE's. But it's hard to complain. This set includes a mess of figures. And I doubt anyone would have turned this set down if it hadn't included the mouse droid, interrogation droid, or trash monster dianoga -- and all of them are high points of the set. One small objection regarding the figures: these are "realistic" skin tone figures, which means not only will Lego purists might object to the pink color on the figures instead of yellow. Plus, it means that any older Lego SW figs are not going to work with these guys, other than masked figures and droids. It's a shame, for me, since I don't have a great deal, but I did have some Imperial officers that I'd love to have for the conference table. But their yellow faces just look wrong next to everyone else.

Fun Factor - ****
Nearly infinite. There's room for imaginative play, there are cool features to put the figures through their paces, there are ways to tweak the set or create your own variations, and plus it's all Lego so you can really just build whatever the heck you want anyway. Great as a display piece, fun as a toy, I'd say it's a great toy for kids, but your kid better do some SERIOUS lawn-mowing if you're giving him or her a pricey item like this...!

Value - **
Tough call. This set comes in at a whopping $400. It's insanely expensive. If I hadn't racked up some serious Lego credits getting friends of mine Christmas and birthday presents, I never would have grabbed this. But if you think of it as an entire collection in one box, rather than just one part of a collection, the price seems worthwhile. It has every playset, every figure, and even a cool vehicle, all in one set. I'd have probably bought this stuff separately and tried not to notice when I reached $400. On the other hand, even breaking this down, if each quarter of the Death Star sold as a single playset for $100, I'd probably consider them overpriced, even by Lego standards. These are
$50-75 rooms, and at $300, I'd call this a fairly priced item, given Lego's high prices. It's huge, it's as complete as you can imagine, and it's an instant classic. But it's no bargain.