The Departed is a perfect gangster movie. It lays the whole set-up out in a way that makes you forget that it's supposed to fall under the gangster movie category. Too often I see films that glamorize the whole lifestyle, when in actuality most of these guys are career criminals whose quality of life is very low. Like Billy said, "It's almost a feudal fucking enterprise." I also like how it realistically portrays the real code of honor: protect yourself. Frank Costello was trading information and people with the real gangsters - the federal government. There is a lot more than meets the eye in this film. I personally take it as a commentary on the close ties between high organized crime and the government and how ridiculous the whole dance is, complete with uniforms and almost religious fervor surrounding the imagined righteousness of one side over the other.
Damn, you nailed that, great post. You're right a lot of people don't think of it as a gangster movie because of the way it's portrayed. The Departed is one of my favorite movies, of any genre; definitely in the top 5.
In the last few years the movies I've watched the most number of times were
The Departed,
Goodfellas, and
Blow, so I'd say they were my favorites of the ones I've seen so far. Some of the stuff I like about Goodfellas and Blow is that some of the more ridiculous scenes that you think are made up are actually true. Supposedly the scene where Joe Pesci shoots Christopher Moltisanti

is based on a real incident. As is the murder in the bar on the made guy. In Blow, Diego Delgado (Carlos Lehder is the real name of the drug trafficker) having his own island, Norman's Cay, was true. It was used to transport a lot of weed and quaaludes as well as cocaine IIRC. Also, George Jung and his friends really did go to Mexico, without knowing how to speak Spanish and looked for someone who can help them get a lot of pot. They also really did just steal a plane so they could fly back and forth with weed. Oh and a lot of that cocaine stuff was true, quantity wise. There's a really awesome book
Cocaine by Dominic Streatfeild that had a couple chapters on it, and I think it was written the year before the movie came out.
I didn't really care for
Casino too much. I felt like it dragged on a bit, and the thing that has stuck with me the most when I think of the movie is how annoying Sharon Stone's character was in it. I guess that says she did a good job acting like a superbitch because it's the only time I can recall being happy to see a man beating a woman (hmmm that feels wrong to say...sorry, but it's true

).
Scarface was pretty good, but it seems so hyped up all the time. I hate the music in it too. I'd like to see the same movie, but with different songs and background music. They could keep the music true to the years the movie took place, but just change so much of it. I feel like the sound doesn't connect to what was happening on screen.
The Untouchables was alright, mostly because of Deniro. There were a few corny scenes in it.
American Gangster was good, but it seemed like it strayed away from the real life events. Frank Lucas nickname was "Supa fly" and I don't think he was the reserved businessy type that he was portrayed as in the movie. At least not to the extent it was in the movie. Nicky Barnes, played by Cuba Gooding Jr., was known as "Mr. Untouchable". He was on the cover of New York Times with that nickname! He set up his own hierarchy, as did Frank, though Frank used his family from the south. In the movie they downplayed Nicky Barnes role a lot, but I guess that was because it was more about Frank Lucas and not specifically the heroin market. Also there seems to be conflicting stories as to what Frank Lucas actually did for Bumpy Johnson, and I don't think they were as close as portrayed in the movie.