Just finished it this evening and I have to say, that Rick Riordan is just getting better at what he already does best: mixing the real world and mythology by taking you through an incredibly fun, action-packed romp.
I really enjoyed how the whole series is setting itself up, especially the introduction of the Roman aspects of the Gods and the 'other' demigod camp (that has a mind-wiped Percy, what a brilliant twist)! I loved reading about the old beloved characters as well (I didn't think I would like Annabeth so much, but I actually dug her quietly determined worry and the fact that she now calls Percy her boyfriend). Thalia as Jason's sister? My mind boggles at the brilliant and wholly appropriate retconning.
The action was fun as well. I enjoyed meeting a whole load of new minor gods. I liked how Riordan manages to 'namedrop' old references, from villains escaping Tartarus (Midea, Midas) to the battle of Troy and Helen's mirror-knife. The fight scenes were gripping, unbelievable, yet realistic at the same time. And I also enjoyed how Riordan kept you guessing before each big Greek/Roman reveal, it was like a little triumph when you guessed it early and a big 'oh yeah' moment when you finally got told who it was. Ah Gaea. You'll be a formidable enemy. It's making me want to research the creation of the Giants, NOW.
My only gripe is that I don't find myself particularly attached to the three new main characters. I find Leo and Jason's voice quite hard to distinguish between one another, and while I'm sympathetic towards Piper, I think Annabeth was a much better version of what she's trying to be (and Thalia and Rachel for that matter). I think two out of the three of them having famous movie star parents also bugged me for some reason. I guess it is difficult to write steadily in shifting third person perspective, but Riordan's style is so distinctive that I guess it's his voice taking control of the whole book, not so much the characters. I didn't necessarily mind this and hopefully each character's narrative will get more distinctive as the series progresses.
All in all, I really enjoyed it. Bring on The Son of Neptune!