The writing is quite masterful. There are definitely some 'love' scenes, but they're very much left up to the reader. As a parent, you'll be able to judge whether it's appropriate for your child. It's worth the read!
If the 11 year old read the Hunger Games, then definitely. Even if they haven't read it, Divergent is a good book. It doesn't have too many adult themes, in my opinion, other than a group of people living in a post-apocalyptic sort of world.