I've just been to see Narnia, and it totally blew me away how well the music worked. I bought the soundtrack last week, and quite frankly thought it was unmemorable muzak. But then when I heard it with the film, it supported it just perfectly, without ever drawing attention to itself.
I've always heard people say that a good soundtrack is one which you don't remember hearing, and that good film music doesn't necessarily bear listening to by itself. I never believed it though. I thought the people who criticised John Williams for always being too much in the foreground were just jealous, but I'm starting to rethink.