I'm currently re-reading the novel right now, almost done, in anticipation for the movie.
The first time around reading it in high school, the novel caught me in its romantic love story. Reading it this time around, the love story is decidedly shallow, along with the rest of the characters, with Carraway being the only one who is privy to the insubstantiality of the lives of the characters.
Now I see the novel much more as a power struggle between Tom and Gatsby, with Gatsby trying to assert himself in a world that can never really accept him, with the possession of Daisy being the means to fulfill his dreams, even though Daisy can never really live up to his dreams. There is a lot to do with reality and unreality in the novel, and it is so subtly done that I think Gatsby is almost impossible to film.
In my opinion reading it now I really don't think Leo is a good Gatsby. At all. Tobey may be alright, yet to be seen.
But that is the least of my beefs, my main beefs being that, judging from the trailer, the film is going to be slathered with a thick coat of Luhrmannian spectacle jizzery all in gaudy 3D, with over the top acting sequences, set to a stupid soundtrack, all of which isn't really felt in the novel.
Will still go and see it though, expectations are low