Now that I think about it, that cliffhanger did do some good deeds to the series:
1. It made me want more, which will probably happen to everyone who reads this, so I think Rick Riordan can look forward to a lot of money in his future.
2. It brought a massive unexpected twist to the story, especially since I expected a happy ending (I thought it was a trilogy! stupid me!!!). This twists does bring out great things in the authors writing, and will keep people begging, wondering and worshipping for his work.
3. It brought life to book, as I felt that the story was being dragged out, and the things that happen felt really repetitive, monsters this, prophecies that, Gaia, Gaia, Gaia every where. Throwing (SPOILER!!) Percy and Annabeth into Tartarus will bring out a more psychological side to the story, and will definitely change the way things are run.
Although I really enjoyed it, I thought that the writing was way to immature for the book. The seven of them-Jason, Piper, Leo, Hazel, Frank, Annabeth and Percy-are all teenagers now, and can't be describe in a way that makes them look like ten-year-olds. And on top of that, six of them are dating (except for poor Leo), and their relationships feels like its five years to young for them. I think that Riordan needs to step up with the writing style, otherwise, he his going to lose some of his older fans, and that won;t be good for anyone.
My favourite character is still Percy, even if he goes a bit weird sometimes, he is still pure awesome. And I love how he is so nice and kind to Annabeth, it brings a real soft side to the once tough son of Poseidon. I never really like Jason, or Piper, they seemed to out of things, like there isn't a world about to end. Jason never really looks past himself, and he reminds me of that Narcissus guy, the one who fell in love himself. Jason seems really similar to him. And Piper is always worried that Jason will run of with some other girl, like Reyna, and even Annabeth, which I believe to be plain stupid. I think Piper isn't that clever, and might be all charmspeak and looks, even if she tries not to be. I think that Frank is a sweet, loveable character, and Hazel seems to bring a bit of mystery, happiness and sadness at the same time, into the story. And Leo. He brings humour, and you can't help be sorry for him, and even more so when he is told he is the seventh wheel, which sounds like he will never has his someone. He his rejected by everyone, and that makes me like him even more so.
The Mark of Athena is a another greek/roman adventure, with your favourite characters, and new ones as well. This book is another great installment of Rick Riordan's mythological series.