True, they could have done a lot better with the first book, but I think you're all critiquing this very harshly. Of course they didn't stay true to most of the stuff in the show. Almost any movie based off of a TV show or book (unless its some sort of TV show that makes a movie with the exact same people), there will be some changes.
All of you are pointing out the bad stuff but where are your thoughts about the awesome fighting? The great special effects?
It's very hard to put 20 25 min. episodes into a movie. They had to sum up the important parts.
Now I'm not saying this movie was all good, because the pronunciation of the names did annoy me. I also didn't like that there was pretty much no humor, except the beginning (which didn't even make me laugh). Only a couple kids in the theater laughed.
All in all, I don't think it deserves the horrible ratings, but it wasn't too great either. From a scale of 1-10, I'd give it a 6.5-7.