I've just come back from seeing this movie in the cinema. Being a devoted Studio Ghibli fan, going to see one of their movies on the big screen was an exciting event for which I had high expectations (I avoided reading any reviews). I am sorry to say that these were not met.
Having never read any of the books this film is based on, a lot of it didn't make any sense. Most of the concepts and character motivations are not given adequate exposition and a lot of things that you think will be resolved and explained as the movie goes on are never expanded upon (or indeed, resolved). Without giving anything away, the main character commits an outrageous action (especially for Ghibli heroes) at the start of the film, but the motivation for said action is not adequately expanded upon and he never really redeems himself (which makes it very difficult to engage with him for the rest of the film). It nearly felt like I was being punished for not being familiar with the source material.
The middle section is very slow moving, in fact nearly all of the action is to be seen at the beginning and towards the finale. Coupled with the lack of exposition on what's actually going on, it seemed like the film was just treading water, waiting for something interesting to happen (and in a 130 minute film, that's a bad thing!).
The ending, while being emotionally rousing and a spectacular set-piece, doesn't really make a lot of sense, as nearly all of the film focuses on a different protagonist than the one that eventually ends up saving the day.
Technically this film is not a patch on Spirited away, Howl's moving castle or Princess Mononoke, in fact the animation is more reminiscent of earlier Studio Ghibli films, such as Nausicaa (however these had wonderful stories to make them instant classics). The only thing that distinguishes it are the lighting effects, which are often superlative.
The music is great and very atmospheric.
Overall I'd have to say that it's worth watching when it comes out on TV, but not good enough to warrant making a trip to one of few cinemas showing it in the UK, or buying it full price on DVD, and this is something that I never thought I'd hear myself say as a die-hard (and now very disappointed) Studio Ghibli fan.
One final thing, this film has no sense of humour. The movie takes itself overwhelmingly serious with none of the "larger than life" magic that people have come to associate with Studio Ghibli.
