I saw The Departed last night, and, uh, wow. It's incredible.
Unlike Bryan, who thought there wasn't any character development, I'd actually call it one of the movie's (small!) flaws. The therapist character was weak and confusing and many of her scenes served very little benefit. It also didn't need a 40-minute expository sequence.
But I agree that it was basically a comedy, though a very twisted one. Several times I caught myself laughing when I should've been horrified.
I don't want to write more for risk of spoilers, so comments will be kept to stylistic descriptions: This was filmmaking at its absolute finest. It treated sound and silence as equals, understanding that each can be as impactful as the other. Even the classic rock soundtrack jumps in and out of diegetic control, especially as Scorsese changes his rhythm in the second half. The editing was precise and tactful, and subtle touches like the use of quick freeze-frames during the climactic shootout (c'mon, you knew there was one) were executed well. Two mutilated thumbs up. See this movie.