As much as I enjoyed this addition to the Percy Jackson world, there were a couple of things that bugged me.
1) Jumping from one narrator to another. It was well signalled, I never got confused with who was doing the talking, but it just annoyed me. I haven't gone back to the other books to check, but either they didn't do it this much or I simply didn't notice it until now. Either way, it bugged me this time.
2) One of my pet peeves is characters who have information and keep it to themselves because the hero/mc isn't supposed to know yet. I might buy it once, if it's integrated well into the story, but in this book it simply seemed like a plot device to pad the book out. Keeping secrets is one thing, but not telling someone something vital because it isn't the time set down for them to know over and over again feels like lazy storytelling to me.
3) I loved the Belgariad when it first came out. Read every book, loved every book. Characters, setting, humour... there was nothing about it I didn't love. But then came the Mallorean. Which seemed to be incredibly derivative, cashing in on the popularity of the Belgariad without the author having to come up with anything much new. Do you see where I'm going with this? Camp Jupiter is an interesting direction to go in but seems a bit 'but wait! there's more!' for my liking.
So why four stars? Because it's a snappy, rollicking yarn with plenty of action, humour and drama. And I'm still a sucker for a good Percy Jackson book.