I'm coming into the same feeling of story exhaustion as I felt with "Harry Potter." I'm enjoying the story, but reading ALL of them in a row almost gets to be a bit much at times. This is when I wish I was reading them when they were first coming out.
A) It gets more exciting for the anticipation.
B) You don't look at your pile of other books to read and say, "Maybe I should've read those in between..."
We find Percy, Annabeth, Tyson and Grover on another quest, trying to figure out the confines of the Labyrinth. Since all of the gods and mythology moves with Western civilization, the great Labyrinth (the one the Minotaur lives in) is in underneath the States.
What I love most about this series is the braininess Riordan puts forth with how the mythology entwines into the story. I sat with Wikipedia for references since most of these stories and characters I've never heard of and it was fun to see how he was going to use the character/storyline.
Although it would be great to understand and know about Greek mythology before reading these books, it's good to at least know the story of Icarus and his father Daedalus...after that, just keep Wikipedia open. Or find Jim Henson's "The Storyteller" where they do a cool live-action actor/Muppet version.