I just finished reading the Gravity Series. I had concerns, initially, that it was going to end up like some weird ESP-laden version of Twilight. Fortunately, Ms. Boyd appears to have far more imagination than Myers.
The books focus on kids at the local high school, so there's a bit of teen-angst. And characters come from both genders, so there's a bit of romance. The kids find themselves trying to sort out a huge conspiracy theory threatening their town, so there's a bit of detective/mystery thrown in, too. And, since one of the main characters sees ghosts, I suppose it'll get labeled as horror, too. I think it's much more action/adventure than horror, myself.
This is pretty good junk food for the brain. It took me a weekend to read all four books (plus book 3.5, comprised of short stories about some secondary characters), but I enjoyed it. I got the first one, Gravity, as a freebie for my Kindle. The others, Uncertainty, Luminosity and Velocity were all $2.99, and book 3.5, Inertia, was $0.99. Frankly $10 for five pretty decent books seems like a fair price.