In general, I liked the stuff they pulled out from other sources and included in the movie. At first I wasn't sure about that Radagast stuff, but by the time it reached its end I thought it was good (minus his ridiculous mode of transportation). I liked the additional stuff in Rivendel.
The stuff I thought brought it down was the stuff that seemed to be totally unnecessary, like having the company pursued by orcs right from the start, the goofy Great Goblin, and the ridiculous action. I mean seriously, how many sequences of falling down bottomless chasms and ending up totally fine can you have before it becomes comical and you diffuse all tension? And the way they did the battle at the end was troubling as well. I guess they needed something climactic to cap off the first film, so I can kind of understand it, but...eh.
But the casting seemed very good (Ian McKellen as Gandalf never did anything for me, but that was pretty much predetermined). Good Thorin and other dwarves, and good Bilbo. Most of the sets and locations were also very good. The parts where they showed the palace inside the Lonely Mountain right at the start were great. If they could have used fewer CGI creatures, that probably would have helped, though.