The plot in a nutshell
It's just before and during the Civil War, and the city of New York is in a war of it's own.  Corruption runs rampant, along with street gangs of every type.  The worst area of New York City, called the Five Points district, is the setting for the majority of the film.

Leonardo DiCaprio plays a young man imprisoned after his father (Liam Neeson) is killed in a gang war by William Cutting, aka Bill the Butcher (Daniel Day Lewis).  Sixteen years later he has returned to the city, and becomes a protégé to the man who killed his father.  His plans for retribution go awry, but in the end a form of justice is served.

This film covers a period of American history normally left out of our text books, and might just convince you to look further into this time in New York City.

DiCaprio's character, Amsterdam Vallon, witnesses the death of his father at the hands of Bill the Butcher during a gang war.  He is sent away to Hellgate prison, an appropriately named version of 'reform' school.  He returns 16 years later to avenge his father.

But here's where the film takes a slight turn from the usual.  Each year, his father's death is still celebrated by Bill the Butcher and the other gangs - it was a great turning point for the gangs, and while Bill might be a cruel, hateful bigot, he is also a man who respects great bravery and strength, traits he admired in young Amsterdam's father.  He plots to kill Bill at this festival.

In the weeks and months prior however, he becomes close to Bill through several situations, and begins to find himself admiring the man he hates, taking him on as a second father figure.  Bill sees Amsterdam as the son he never had, and the two develop a deep relationship before the inevitable disintegration and final challenge.

This is an excellent period piece, with lavish sets, fantastic cinematography, and excellent costumes.  You are brought into the period seamlessly, and Scorsese does a marvelous job creating an epic feel.  This is Scorsese on top of his game.  He brings us a period of American history we rarely hear about or see, and weaves the facts with the fantasy to give us an entertaining and thought provoking film.

Both DiCaprio and Day-Lewis do an excellent job with their roles, and you can truly see the bond form between them as their relationship progresses.  Cameron Diaz, as the necessary love interest, doesn't have much to do, or does she do what there is particularly well.  Her accent tends to drift about quite a bit, but the rest of the cast was extremely believable, and the supporting roles by Jim Broadbent, Henry Thomas and John C. Reilly all add to the overall film.

Rating - Buy It
This is one worth having around to view more than once, although at a run time of about 3 hours that might not be too often.  Of the Academy Award films released so far - Far From Heaven, About Schmidt, The Pianist, The Hours and Gangs of New York - this is my clear favorite.  Chicago is yet to be released, but while I don't hate musicals, I'd be extremely surprised if I enjoyed it more than Gangs of New York.

Spoiler Laden Thoughts
There aren't any plot points to discuss here - I guess it's not true that only bad movies have no need for a spoiler discussion!