I didn't think I'd like this book when I started reading it. The opening scene nearly put me off the book completely. Daphne grated on my nerves every step of the way. After the first few chapters, though, the story settled down, and started actually building the plot.
The plot itself was nothing new (boy is reincarnated hero who is doomed to fight the same battle for all eternity), but the characters were interesting enough to keep the story entertaining. Aside from Daphne's constant "creative" cursing, the other characters were all pretty fun. Even the villains. Well, Anna, at least. All of the others were stereotypical bullies. Anna was awesome, though - cold and calculating, and playing everything to her advantage.
Victoria was one of the best parts of the book. The other characters were fun, but Victoria was definitely one of the stronger ones. She had fun dialogue, her back story (or what is given of it) is interesting, and I swear her father has to be related to Foaly from Eoin Colfer's Artemis Fowl books. British centaurs...good times.
Another thing that I liked about the story was that there wasn't a heavy-handed moral thrown in there. There was no "the power of friendship overcomes all odds" message tacked on. True, Alex couldn't have resealed the evil without his friends' help, but he was also helped by people who weren't his friends, who played just as big of a role in things as his group did.
While the ending could be considered a cliffhanger, I think it did a fine job of ending the book. It could easily stand alone as its own story, although there are more books in the series. The ending ties up the first book nicely, but also provides a segue into the second one.