I love Diana Wynne Jones' Howl’s Moving Castle for about a thousand and one different reasons. But this isn’t a straight book review, and I'm only going to talk about one reason I love this book. And I will spoil things just a little bit. If you haven't read the book, beware.
Sophie is timid when we first meet her. I don’t believe she is naturally timid. The world has boxed her into a very specific role, and she has worked within those boundaries so well that she has shrunk down to fit them. Until the day she doesn’t want to fit into her boundaries anymore. She says something very ill-advised to a very bad sort of person, and is cursed to live as an old woman. Old age turns out to be a good experience for her; she becomes bold and sharp-tongued and stubborn.
Howl falls within the realm of the classic Byronic hero. He’s sly and clever. He’s melodramatic. He’s a proud coward. Sophie calls him a “slitherer-outer” because he consistently avoids serious conversations and decisions, instead putting them off until someone else handles the decisions for him. Sophie attempts to manage Howl, with mixed and often hilarious results.
There is a love story, but it is a very slow-played love story. They aren't blind to each other's faults. They have to deal honestly with each other and with themselves before the "will they/won't they" dance ends in "they did."
When they show up in two more books, they remain happily married. He makes life difficult but interesting and she keeps him amused and in check. They remain very much in love while starkly aware of each other’s strengths and faults. Most writers fear that this makes a couple boring, but DWJ didn't. The "will they/won't they" dance ends, but another, better dance follows it. They keep bickering and adventuring and finding new ways to drive each other thoroughly and blissfully insane. DWJ deftly avoids the all-too-common trope in which a married couple gets bored with married life and has to look for outside of it to spice things up.
This is a rarity when I think it should be the norm. And it's one of the thousand and one reasons I love Howl's Moving Castle.