I think the best part is the background lore. I liked the explanations of the witches, sorcerors, and demons. Armstrong's world of supernaturals sounds like a very interesting place, and I'm looking forward to reading the other two books.

Paige and Savannah's relationship is quite interesting. How Paige managed to not choke the life out of Savannah, I'll never know. Wow. I hope S's hormones fall into line ... for Paige's sake. :P They have sort of an Obi-Wan/Anakin type of relationship where the reckless student is more powerful than the beleaguered mentor. So when Savannah causes trouble, the audience isn't sure to what extent Paige is going to be able to solve it, and it's an interesting cause of tension.

The romantic element was predictable and thus pretty uninteresting. The story could've done without it altogether, and may have arguably been more interesting without it since the motivations of the love interest would be further clouded.