Yeah, they kinda have to make some changes, or those who have read the book(which you should before you see it) will know exactly what happens all the time. The one change that I really thought was unnecessary, though, was bard using that ridiculous giant ballista of silliness to slay the dragon. It's so iconic that he uses his own bow to slay the dragon!!!
other than that, though, the movie was epic! I imagine in the TABA wave, there will be a Smaug vs Bard set with a hopefully brick built smaug, and bard with his crossbow of silliness.