It wasn't bad. I enjoyed the photography and was generally engaged through the whole thing. The actors are starting to look a little old for their parts, but that bothered me only a little. I did find the ending very abrupt and unsatisfying (though I do know what happens later because I read the 7th book). Overall I'd say it was okay, not great.
As I recall, the 6th book was also the weakest of the novels so maybe it was the material as much as anything. It's more a "connector" story - good for prepping you for book 7, but doesn't stand up as well on its own. I read the books a while ago so I can't remember all the details of the book versus the movie.
I was bored during this movie, and became increasingly resentful that I wasted $12 and my Saturday afternoon to see it. The characters were completely unbelievable - no one could be that stupid. They were so 2D that they did not bring me along as a viewer. I just kept thinking this is ridiculous. I also did NOT enjoy the grotesque violence that appears at two points in the film. This is supposed to be amusing? I really hated this movie. Don't waste your time.