I'm a sucker for special effects, which look spectacular in the trailers.

I get what you mean about changing things up a bit. In LotR I sat in the theater thinking, 'wait, that's not what happened in the book' but I was still enthralled by the movies. When I went to see The Davinci Code, though, I was surprised that I was kind of bored simply because they followed the book so closely that there were no surprises ;o)