CAUTION: There are **spoilers** in this post.
Howl's was beautiful visually. However, as has happened with other Miyazaki films, such as Spirited Away, Nausicaa, and Princess Monoke, there were parts that were just bizarre to me. I don't know if that is due to a lack in the story, or due to the cross-cultural jump. Mononke and Spirited were fascinating to me because I learned about Japanese folklore, but that didn't change the fact that there were parts that were a little difficult for me to follow.
In his review Skar wrote:
A big part of understanding characters in a story is seeing what they do. But those actions have to fit in with the story, effect must flow from cause. In Howl's Moving Castle the characters do inexplicable things on a regular basis. And when I say inexplicable I mean it. You're left staring at a big screen in a darkened theatre wondering, "What? Why is she doing that? Why is that happening? What the heck is going on here?" I'm sure there were favorite scenes from the book that had to be included in the movie to avoid rabid fans complaining bitterly about the things that were left out; unfortunately, some of those scenes fit like a pair of shoes fit in the refrigerator. There's no problem with space, but you're left with the troubling sense that you really don't know what's going on. As I said, those of you who read and liked the book will probably be able to unconsciously fill in all those gaps and get a lot of enjoyment out of the movie.
Surprisingly, I believe that having read the book will not stop you from asking "What? Why is she doing that?" There were plenty of moments like that for me--particularly with the Witch of the Waste, who was entirely changed in the movie, and not (in my opinion) for the better. Having read the book only helps give a background, because it is only the basic structure of the world and the characters that Miyazaki uses. Miyazaki changed a lot of the plot to make it his "own" (which, to some extent, I am okay with--I believe adaptation requires a director to do just that), but I feel that a lot of the gaps in logic came from his changes.
Even the ending, which Skar called "deus ex machina." Miyazaki left out an important fact of Sophie's character--that she is a powerful witch in her own right with the power to give life to inanimate objects. She doesn't realize she has this power until the end of the book, and it is this power that makes it so she can re-animate Howl's heart without killing him or Calcifer. Miyazaki's ending, lacking this, was more of like the answer to a riddle. Once Sophie finally understood that Calcifer had Howl's heart, all she had to do was put it back inside him. Which begged the question--why couldn't Howl do it himself? It made more sense in the book, because Howl and Calcifer needed Sophie's magic.
Still, even with some gaps in the logic and a bit of meandering in the plot, I still really enjoyed the film. And it WAS beautiful visually--it makes me miss traditional animation, now that Hollywood is doing only CGI films (and often rather ugly ones at that).