First of all, I'm moving!
And Percy Jackson provides just the right kind of story. I remember thinking when the series first came out that is sounded like a way of cashing in on the success of Harry Potter, and truth be told it's difficult to avoid that feeling. But kids who are "different" at some sort of boarding school is a children's literature trope that long predates JK Rowling.
I'm getting off topic. Percy is just finishing sixth grade at the start of the novel, and trouble always seems to find him. Which is why he gets sent from school to school. Turns out this is because he is the son of a human woman and an god from Olympus. Oops. And not just any god.... So while a huge part of the story is about Percy's attempts to fit in and find his place in the world - difficult even in a camp filled with half-bloods like him - what drives the plot is his efforts to, well, save the world by taking on an almost impossible mission. And in so doing, clear his name and gain his father's recognition. Plenty going on, and pretty much all the kind of themes that resonate with kids Percy's age.
But readers of all ages can find enjoyment in Percy's story. I struggled a bit with the 12 y.o. male narrator and a writing style that I found too much that of a 12 y.o. male. So my problem, not the book's. But once I accepted Percy's voice for what it was, I had a great time in his world. I'll be looking for the rest of the series. (And Riordan's series involving the Egyptian gods, I believe!)