I really enjoy this series, though not more so than the Greek stuff he writes. Kane Chronicles definitely feel pitched towards an older audience. I didn't like this one as much as the first in the series, which was a welcome change.
This is just going to be a tiny little review because I don't want to give anything away.
This one picks up not long after the first one ended, and introduces a much larger cast of characters, which is where my main problem with this book lies. Rick Riordan likes to create large casts, and while he gives them interesting information and histories, he also lacks the ability to flesh them out as much as I would like. He's definitely gotten better over time, but I had this problem even when reading Percy Jackson and Heroes of Olympus (though HOO does a much better job than either of the other series' do).
Overall the story was good. I loved how funny it was- actually made me laugh, which is becoming a rare thing for books to do- and I love the magic system in this series. It's one of the major draws. Additionally, it seems like it was written for an older audience. It deals a lot more with death and dying and romance than the other series' and also deals with race a bit (though not as much as the first one did).
If you weren't a fan of Percy Jackson, you might still like this series. It's quite a bit different in many respects.