The movie made me realize how much Catching Fire is my favorite of the Hunger Games trilogy - it opens up the world of Panem and the greater political struggle beyond what happens to Katniss and her loved ones. To be fair, the first movie opened up that world too, more than the book did — but in Catching Fire, Katniss becomes more aware of the greater political stakes around her, and as our main point-of-view character, that’s important. The movie also did a much better job than the book did of making Katniss explicitly a rebel, someone who recognizes the consequences of defying the totalitarian government and who eventually chooses to do so anyway. Actually, this is more than “did a better job” - the movie breaks somewhat from the book’s characterization of Katniss as someone who persists in being willingly myopic about the bigger picture and is (understandably) focused on her short-term survival instead of long-term rebellion, even when her actions foment that bigger political movement.
Two scenes really made a difference in the movie. (Spoilers ahead.)