All of the books (not so much the first one), have somewhat of a sexual undertone. In the first few, it's about not having sex - not because they aren't married, but because they can't lose control because Edward is a vampire. Later there is sex after marriage (a different category to me, because I've always told my kids that sex after marriage is a good thing, but, although vague for an adult, it is a little too sensual for a preteen book, IMO).
What I think worries me even more is that the second book is about choosing suicide when you lose the one you love. And I can't see any way of the movie not being pretty clear about that as well, which makes me worry because teens take break-ups so hard, and it's so easy for them, especially boys, to get depressed, that it scares me that they think suicide would be the ultimate sacrifice for love.
BTW, I just finished reading the second book a second time last night! I am re-reading the series, lol, so I obviously love it! What's really funny is none of my three kids (girls ages 20 and 19 and a 15 year old boy), have read it! They did love the movie, though.