By reading a lot of novels in a variety of genres, and asking questions, it's possible to learn how things are done - the mechanics of writing, so to speak - and which genres and authors excel in various areas. ↗
'I Am Number Four' definitely borrows from a whole bunch of genres and has a whole bunch of different themes throughout. And I think if it was just one stale two-dimensional thing then it would be kind of boring. And I think they did a fantastic job. ↗
Some genres I'm not a huge fan of but there are always exceptions that break the rules. There are always a few people doing it in a way weird enough to grab my attention. ↗
Dismissing fantasy writing because some of it is bad is exactly like saying I'm not reading Jane Eyre because it is a romance and I know romance is crap. ↗