I actually really liked the movie for the most part. There were a few things I didn't like, but most of it was good. The main thing that detracted from my enjoyment of it was the length, but any movie over about two hours will have me getting restless, especially in the theater.
Stuff I particularly liked:
-Portrayal of Bilbo's character and the dwarves
-CGI visuals were mostly very good, I thought
-Thorin was different but a more interesting and relatable character than he was in the book; I approve of this change
-More tension between the dwarves and elves than in the book; made an otherwise somewhat dull Rivendell scene more interesting
-The troll scene departed a bit from the book, but I thought it was pretty good; I think some people forget how goofy and bumbling the trolls were even in the book
Stuff I didn't like:
-The Goblin city scene. This is one part that I think should have stuck to the book a little better: Bilbo is with the dwarves, Gandalf kills the Goblin King, then they all run through the tunnels until Bilbo gets dropped, leading to the Gollum scene. That scene was good in the book and would have been fine on the screen, so I don't see why it had to be changed so much.
-The Goblin King looked like some cartoony crap out of a Star Wars prequel.
-The one-armed goblin had too important of a role as the main antagonist. I think this was done to create a more cohesive story with a clear bad guy, but I don't think this was really necessary.
-Galadriel's telepathy and teleportation abilities: Why even invent that crap, especially for a character that wasn't even in the book?
-Radagast's portrayal. I didn't mind at all that he was inserted into the plot, but I always visualized him totally differently, as sort of a burly, jovial fellow, not a nervous little crackpot. I may have confused him a bit with Tom Bombadil when I read the books, though.
-The overall tone. The whole film seemed confused about what it was supposed to be: at times it would try to come off as epic and serious as the Lord of the Rings trilogy, but then there would be some lame fart joke or cheesy one-liner. I'm OK with a lighter, more humorous tone than the LotR trilogy--in fact, it needed to be, since The Hobbit is lighter and more humorous than the LotR books--but fart jokes, snot jokes, and lines like "croquet's a fine game, if you have the balls for it" and the Goblin King's "that'll do it" (that really made me cringe) do not represent Tolkien's humor at all. They should have stuck with jokes about bumbling trolls, fat dwarves, and Bilbo's agitation. More feel-good humor than laugh-out-loud humor, but that's what The Hobbit is.