It was *awesome*.
Despite adding pieces here and there (most notably we see Radagast making the discovery of the Necromancer's presence in Mirkwood, and a meeting of a significant portion of the White Council following that news), Jackson stuck closer to the original than he did in the LotR movies.
His major changes were to make some events more active than they were in the book -- i.e., where things are more talked-about than done in the book, here they're more done. Perhaps the largest individual change was in the Troll sequence. In this version, Bilbo goes first to try to free the horses, can't untie Troll-made knots, and gets caught when he's trying to remove a troll-knife to cut the ropes. The Dwarves do NOT do the stupid thing of coming one at a time to get caught; once they realize that Bilbo's not coming back, they charge in en masse, and do a pretty good job; but unfortunately they're apparently not fully used to fighting things that badass yet, so they get caught and tied up. Bilbo manages to talk to them long enough to stall for time (as he notices Gandalf approaching), giving Gandalf the chance to get into position and do the "Dawn take you all!".
While this is certainly different, one of the things it does is start to establish Bilbo as having some agency, courage, and willingness to ACT. It also makes his later actions more believable and part of his development.
There's some other minor changes, some only a matter of changing the order of things. There IS one added subplot which derives from another part of the appendices, but he integrates it well.
The movie STARTS with a prologue that shows us Erebor at the height of its power, and then its fall and destruction -- without showing us more than the tiniest glimpse of the Dragon Smaug himself. This gives us a look at what the Dwarves have lost that's a LOT better than having it described to us, and also shows us (rather than tells us) the reason for the Dwarves' dislike of the Elves (and vice versa) in this particular case.
I wouldn't say I liked this *quite* as much as The Avengers, which was just filled with awesome moments from the time it started to the time it ended, but it's way up there. Highly recommended, except for the purists who can't stand anything being changed. For those, God No, don't go, and save yourself the annoyance and us the whines.
Also, we saw several previews for some potentially interesting movies, such as Jack the Giant-Slayer and Oblivion. With respect to the latter, though, Tom Cruise has either sealed a pact with the Devil for Eternal Youth, or special effects and plastic surgery have *REALLY* come farther than I thought, because he looked hardly older in the Oblivion preview than he did when he played in Top Gun!