I read the books and enjoyed them. But, I'm not getting my hopes up for the movie. You know how it is; the books are almost always better. I figure, if it ends up being good, I'll just be pleasantly surprised instead of being sorely disappointed.
Stephenie Meyer did work on the set and everything though, and she approved the script, so it shouldn't be TOO off from the book's plot. I know there are a few minor changes though.
And yeah, the cast isn't what I pictured when I was reading the books, but it's not something I think anyone should really be too upset about. It is very impossible to get the perfect Edward, because everyone has different ideas of what an ideal guy looks like. (And same sort of thing goes for Bella and the rest of the cast as well.) They just picked the cast based on the actors' talent and chemistry, which should be better than just picking them based on looks.