The action scenes are too long, and the survival rate too high, trying willing suspension of disbelief. I can only rate it a B.
Cheating Azog as a Big Bad for the movie does no harm, nor does behind the scenes chatter about the Necromancer. Radagast is charming in a way pretty reminiscent of the tone of the book. Making Thorin a tragic hero doesn't hurt, nor does giving Bilbo a temporary save. This kind of padding might have dropped the rating even further, down to C.
But the big dramatic moments of Bilbo deciding to go and to spare Gollum were done quite effectively and gave the movie some weight to keep it from drifting away on gusts of boring "action" set pieces.
PS They seemed to have showed trailers for every big budget 3D FX movie for the next year. The only one that seemed really interesting was Man of Steel, which was unexpected.