My short review:
The book was better, no contest. The movie was great, but it lacked the raw emotion and perspective of Suzanne Collins' writing. They left out quite a bit (the ending wasn't anywhere near as good as the book), but the changes were understandable. Jennifer Lawrence was great, and I was pleasantly surprised by Josh Hutcherson's performance. I wasn't really feeling Woody Harrelson or Liam Hemsworth, but they did an adequate job.
The violence was pretty mild, but seeing teens murder each other did affect me more than I thought it would. Especially when the stronger kids are laughing as they slaughter the weaker kids. Seeing the violence on screen, as opposed to reading it, was intense.
All in all, I'd recommend reading the books first. The movie is great as an adaptation of the novel, but not so good as a stand alone film. Oh, and if you go, be sure to bring tissues. There were at least three parts I choked up at, and I never cry during movies.