I started reading this with an open mind. The plot sounded really interesting and the cover is pretty. I was bitterly disappointed. I didn't enjoy this at all.
Ari's character was one that I wanted to like but I just couldn't get past her complaining about how awful her life is. 'Oh, I'm going to die at 21!', 'My hair keeps growing!', 'My eyes are weird!' etc. Not actual quotes, that's was just the general feel of it for me.
The plot is also quite silly in places, especially when Ari experiences her first uber-headache. She wakes up in a restaurant and snogs Sebastian's face off. Then they're a couple. Then they're not. Then they are again. Then she tries to hump a Vampire...
One redeeming factor for me was Violet, a little goth girl with sharp teeth and a pet alligator. Violet is really sweet, like the perfect kid sister - plus she has the handy fighting skills.