I started them while I was traveling for work and ran out of reading material in the middle of the week. That was back when only the first two books were available in paperback. It was a struggle not to purchase the third in hardcover, but I really didn't want to have to carry it back on the plane. I read a library copy when I got back home and then bought it in paperback when it came out. I've bought the rest in hardcover (paying extra for the recycled paper versions from Canada).
I think they're quite readable, but not only do I read a lot of science fiction and fantasy, but I also read a lot of "young adult" fiction. There are authors writing in similar genres who I think are better writers (Diana Wynn Jones comes immediately to mind), but the books are pretty good. The fourth was probably my least favorite.
I agree with HarryT that if you haven't tried them, there's no point in criticizing them. If you have tried them and didn't like them, fine-- no book pleases everyone.
