The book starts off differently than the other two. Whereas the previous books begin at the start of summer and are heavy in exposition, this one starts in the heart of winter and gives exposition the finger. At first it's a bit disorienting, seeing the end of the previous book ends introducing the human form of Thalia. This one picks up with Percy, Thalia, and Annabeth going to meet Grover at a military school, as he had found a couple more half-bloods. There's no immediate explanation of why Grover is searching for half-bloods again, or how they all got so buddy-buddy with Thalia. It does explain, but briefly, and not right away. Don't get me wrong, this isn't really a complaint. It was actually somewhat refreshing, not having to have things I should already know beaten over my head.
Anyway, there's a scuffle, and Annabeth ends up kidnapped, while Percy, Thalia, Grover, and the two half-bloods he found--Bianca and Nico di Angelo--are saved by The Hunters (or Huntresses, rather), the elite group of warriors led by the goddess Artemis. Artemis goes off to hunt a powerful monster that the bad guys are after, leaving her followers, including the tough Zoe Nightshade, to go back to Camp Half-Blood. They hitch a ride with Artemis' twin brother Apollo and make it back to camp. One thing leads to another, and there's another prophecy and another quest. A team of five must search for the now-kidnapped Artemis, though with the knowledge that two will die and one will hold the burden of the Titan's curse. And then there's the whole issue of rescuing Annabeth, which Percy takes to heart, especially when it's declared that he's not one of the five going on the quest.
Almost right away, the book seems darker than its predecessors. There's still a lot of fun action. I particularly liked the brief fight between Percy and Thalia early on. And speaking of Thalia, if there's one thing that I would have liked to see done just slightly differently, it would be her relationship with Percy. Or rather, how Percy perceives her. The first half of the book sets it up as if Percy is going to have this on-going rivalry with her, where everybody follows Thalia and she gets all the glory, leaving Percy behind as just some other, average hero. But the latter half of the book drops this. I thought it would have really played better if he would have gotten more angsty with her and her sudden spotlight... kind of like how Ron got with Harry in Goblet of Fire, I suppose.
And speaking of Harry Potter, there were still a few parallels, but they're getting further and further away, much harder to just point out and go "that's totally Harry Potter." There really wasn't anything major or blatant, at least not that I can remember. So that's a good sign.
My favorite thing about the previous book was Hermes, so it's not that much of a surprise that some of my favorite bits for this book involved other gods and goddesses, namely Artemis and Apollo. We also see Aphrodite and Athena up close and personal for the first time, too. Though what I really liked was the reveal of the General. Strangely, I picked up on a certain myth going on earlier, but I didn't make the connection until right before it was revealed. Similarly, I had a hunch of who Nico and Bianca's immortal parent was for most of the book, but I think only because I've been hoping to see a child of this particular deity since the first book. I also think Rick Riordan handled the clues much more subtly for them than he did Percy, which he bashed repeatedly over our heads for over 100 pages of the first book.
One interesting note that I'd like to bring up that I haven't yet in any of these reviews is something I noticed that is rather prevalent in these books. Mr. Riordan quite often likes to make sure that the characters, usually Percy, grabs anything important from wherever, because he/they have a feeling that he/they "won't be returning to/won't be seeing this place again and/or for a long time." It just seems too coincidental that Percy or the group just know, for no reason, that they're about to be forced from wherever they're at and so they better take their things, because they'll need them for the rest of the plot. I've seen this happen in each book so far, sometimes more than once (I think it happened at least 2-3 times or so in the second book).
A few final notes... the book was not only better written and more intricate than its predecessors, but it was also funnier. I loved the Hoover Dam chapter; it actually made me laugh out loud. Also, for the first time, the book didn't feel self-contained. There were some things left hanging, such as Clarisse's quest, the di Angelo "lawyer," or anything about the mortal girl from the Hoover Dam (I know she has to be important later... too big of a deal was made of her). And speaking of things important for later, the Lotus Hotel came back into play, though it still really wasn't explained. Its magical properties were used (rather cleverly, might I add) for plot purposes, but I'd still like some kind of explanation of its existence. I need to go out and buy the last two books (I only got the first three), because I really want to start up the fourth. There's so much I left out of this review that I liked (from Bessie to Blackjack, and even Dionysus... who, though I had a small quibble about regarding his interesting though almost completely out of nowhere explanation of why he hates heroes, has a good moment toward the end of the book). So again, I loved this third installment. To me, it was clearly the best thus far, and I can only hope the next two are even better.