Finally saw the movie, and stayed out of this thread until I did.
Most changes seemed to be cut for time and streamline the story. It's already 2 hours and 22 minutes.
The rest of the changes were made for a PG-13 rating. No nudity from Katniss and reduced visuals of violence on-screen.
There are some trivial things changed, but most fall under those 2 reasons.
The movie was amazing.