This review will contain spoilers!
In many sentences:
I took my time reading Brave Story in part because I finished it in November, while I was writing for NaNoWriMo. However, it was also just a long, slow reading, and it never really compelled me to keep going. I didn't dislike it, but I was never really captivated by the story, and that's probably the biggest problem I had with this book.
The first 2 or 3 hundred pages, before Wataru really gets to Vision are definitely the slowest. Ultimately they are worth it, because it presents a compelling reason for Wataru to go to Vision, and it provides context for the decision at the end (saving Vision instead of changing his own destiny) being a difficult choice. If we didn't understand that Wataru was making a hard choice, the ending would be awful. As it is, it builds well and the ending is strong.
The entire theme that Wataru must learn to handle whatever destiny throws at him, rather than expecting this one change to make the rest of his life perfect, is also handled well. Yes, it does come right out and say all of this, but it gets there in such a way that the lack of subtlety wasn't annoying. If we didn't see how Wataru came to these decisions, how he developed friendships that were meaningful in Vision, this would have been terrible, but as it was it worked.
Unfortunately, while there are certainly some good elements to this book, the fact that this fantasy world didn't grab me the way great books do, leaves me a little indifferent to it. I wouldn't actively discourage anyone from reading it, but I won't evangelize it to those wanting something to read either. So, in the end, I don't recommend this book, but if you want something that explores these themes, and that takes place in a unique fantasy world, it has enough positive aspects to make it worth reading. Another way I can put this is, I can't recommend it to anyone else, because I don't want to read it again.