Finished the series! Wohoo! And I really love the way they ended. Yeah, maybe I was able to predict some of the ending (like 6 books ago) but there were a few good surprises. And naturally it sets up a whole other series at the end. I think this is a fun series and I love that the ending brought it to England and had a lot to do with Shakespeare. I think these books are so educational and my kids will definitely be reading them, although not for a few years. They can get pretty intense, so I'd say upper elementary school/middle school ages would like it best, but of course, always depending on the individual child.
It was a fun journey, and it was a nice change to have 10 books come out in such a short amount of time. The author switches were well done, so in some books a style difference wasn't even detectable. I wish they'd all been written by Rick Riordan, but he's a busy guy. His new book The Lost Hero is coming out next week (new Camp Half-Blood series! Hooray for Greek Mythology!!!) and I'm looking forward to that.