Count me among those who felt lukewarm about the movie. I didn't mind the light-hearted tone, and some scenes (the riddle game in particular) were actually pretty effective. But there were two major problems that I felt dragged the movie down. First, they dragged in too many extraneous side-plots and tie-ins to the larger Middle Earth mythology. The Hobbit is a small-scale story, and adding too much epic background just dilutes it - whether you see him or not, Smaug should be the looming threat in the back of our minds, but oh shit, the Necromancer's coming back, and oh no, Captain Hook the Orc, and dragon? What dragon? Oh right, there was also a dragon in this story. That's cool, I guess. But seriously, what's the deal with this Necromancer?
The second major issue was that Jackson, with his characteristic lack of restraint, felt the need to turn absolutely everything into a major action setpiece. For example, from what I recall, the Rock Giants get barely a passing mention in the book - they're just there to lend a bit of fantasy colour to the storm on the mountain. Jackson turns them into a full-blown extended action scene, and yeah, it's pretty cool, but the problem is that it you can feel that it doesn't belong in the movie. It does nothing to advance the plot, and if it was cut from the movie, you'd never notice. It's just there, and all the extra padding just bleeds the dramatic tension out of the movie. It feels more like an amusement-park ride than an attempt to tell a story.
Okay, I lied, I actually have three major objections. Jar-'Jar the Brown? Seriously?
So, yeah, I didn't hate the movie or anything, but at no point did it have me going "F--- YEAH!". And it really should have.