I watched the movie first, which was all kinds of a mistake. The kid was completely obnoxious and stupid, as were his supposed guardians. They never explained anything to him--like, hey that dark rider guy might send other people after you or fake the voices of your family to get you to open a door for him that only you can open. And, even after the rider dude had shown he obviously wasn't a nice guy (and therefore probably was going to swipe the magic jewelry from the kid and then send him straight to hell), obnoxious kid was still falling for his tricks. I know it was a kids' movie and all, but even as such it was pretty much insulting to my intelligence.
I liked the characters better in the book, but I thought it still had problems. I'm a big fan of fantasy books, but I think if you're going to introduce magic there have to be rules. You can't just invent a spell when it's convenient to advance the plot and still have a great story. I enjoyed bits and pieces--like the part about the Walker--but all in all it was just too unfocused. I don't think I'll take the time to read the rest of the series.