I saw it last night...I'd like to chime in with my thoughts. Tried to keep it spoiler-free.
Jennifer Lawrence, I think, nailed it. She did very well at conveying all the changes that Katniss went through over the course of training and the Games themselves. Especially during the Games in the book, there's not much dialog but boatloads of exposition and insight into what's happening in Katniss's mind that would have been hard to do without voiceover. Lawrence was able to show, subtly, the changes in Katniss throughout the games.
The actor that played Peeta wasn't given much to do in the movie. I can't really knock the kid, although the acting seemed pretty...basic. Peeta doesn't really get that interesting in the book until quite a ways into it anyway. Not sure they could have made that work in a movie at all.
The actor that played Gale was terrible, IMO. Waaaay too emo-y for me. Without giving anything away, I have trouble seeing how well that will translate as they turn the next two books into movies.
Woody did very well. I've liked him in most everything, though, so I'm jaded. Lenny Kravitz was actually VERY good as well. Kept it extremely low-key.
Also, if you don't like shaky-cam (which I don't), be patient through the beginning. It's used WAAAAAAAY too much early on. Like, the first ten whole minutes of the movie. It backs off considerably and is then used pretty judiciously throughout the rest.
Donald Sutherland wasn't given a ton to do, either, but made the most of it. Hopefully he's signed as President Snow for the rest of the movies.