I haven't read Middlesex, but I have read The Virgin Suicides many times. I actually bought the book new in 1993. Anyway, even if you have seen the movie, read the book. The movie actually followed the movie really well, but there is still a lot more in the book. The story was really good, and it made you really feel for the characters.
I tried to read Middlesex when it first came out because I loved The Virgin Suicides so much, but I just couldn't get into it. Maybe I'll try again.