Yeah, the ending was really good, butHonestly, i think the movie was too reliant of it. The whole movie was just "wait for the twist", it wasn't actually fun to begin with. In fact, most of the dialog was pretty boring, and only had some value in the end.
Not only was the dialog boring, the characters were just foul-mouthed, tough-guy thugs, although Spacey's character is interesting. So it's next to impossible to care about them. Let 'em all kill each other for all I care. Yes, the ending is clever, but everything that goes on up to that point isn't really worth sitting through. The movie's seriously overrated.
My 175 (or so) Favorite Movies:
http://www.imdb.com/list/ls070122364/

So what? Since when does that mean a movie isn't any good? It did win for best original screenplay and best supporting actor. It also won best movie at the BAFTA's.

it wasn't even nominated for best picture

I completely disagree with you. I think the characters, their interaction, the dialogue, the look and the story itself are great. Watching Casablanca in the same night would only make it look like a greater masterpiece to me, because that movie sucks so hard.