I finally read the second book of Riordan's Kane series yesterday. My feelings about it largely mirrored my feelings on the first book: I didn't think the principles acted much like teenagers; the romantic aspects fall a bit flat for me, given the ages of the characters; the story was very well-constructed; and the mythology used was interesting. I did like that Sadie and Carter acted a bit more like siblings (we got to see more than just rivalry), and I liked the new characters.
One minor thing that bothered me was in the telling of the story of Akhenaten, I'm not sure why his name was spelled Akhenaton. I haven't done a lot of reading about it, but the last time I read about him, it was spelled Akhenaten to match Aten. And I believe it was originally Akhenamon (to match Amon-Ra), but he changed it to Akhenaten to show his new belief.
Anyway, as a quest novel it worked fairly well, although some of Sadie and Carter's choices along the way were rather... peculiar. Perhaps that was a nod to them being teenagers, but deliberately not going after your goal when you're in a huge hurry was... odd, I guess.
Still, it did play out well, and left things well positioned for the third book (which I already started, this morning). I'm looking forward to The Serpent's Shadow.