I've watched the anime movie a couple (dozen) times already so I thought I might as well read it. For those who only watched it, you're in for a treat. There were so many ways that he anime plot veered off from the original storytelling and where the movie itself was confusing as hell, the book just didn't even have those parts. It is a wildly intricate story with lots of details, hilarious witty insults, and some unique blown-out-of-proportion characters.
The book itself is definitely the better of the deal even though the movie lends some interesting elements never found in print. Howl and Sophie reappear in House of Many Ways in the later years. I wonder what they're up to?