I knew about this book (mostly because there was a movie, too), but it wasn't until I started putting together a "Neil Gaiman Recommends It" reading list that I finally bought it. Irrespective of the fact that I bought it about five years ago and only just now got around to reading it, that's a pretty high recommendation for me. What with the floating castle that's constantly moving, the falling stars, the witches and wizards, and the curses that make young girls into old women, I can see why it's a "Gaiman" book.
It's also clearly a juvenile book. I've started noticing that writers of juvenile fiction spell things out a little more obviously, with more telling than showing, with characters who are a bit one-dimensional, and with less subtlety to the story. Howl's Moving Castle has the telling, but it also has the subtlety of a well-told tale. The direction wasn't obvious, and the characters had more layers than I would have expected.
I love the imagery and the world-building here, and the way that the castle had doors that led to different places fascinated me. The characters of were charming (even Howl, once you got past his insufferable attitude), and the plot regarding Howl versus the Witch of the Waste was engaging enough to keep me reading. It just read so much like a kids' book that it's hard to recommend it without reservation.
What really carries the book is the charm of the characters, and that's part of why I rated the book as highly as I did. I'm interested enough to read the next two books in the series, though I understand they're pretty different from this one. So long as Sophie, Michael, Calcifer, and Howl are there, though, I think I'll be good.