This set was recommended to me by a 9th grader, and I'm giving the hardcover set to my granddaughter on her 10th birthday. While the writing style is not up to my J.K.Rowling yardstick, the books offer good characters and an unusual premise. Percy and others are "demigods", meaning that one of their parents is a Greek god. Thus, Riordan also brings young readers into the world of mythology while providing an entertaining action storyline.
As with the Potter books, one of my favorite characteristics if that the books focus on friendship rather than moving into any type of romance. In book one, THE LIGHTNING THIEF, Percy (short for Perseus) is 11, and becomes a year older in each book.
The set of 5 is rather uneven, with the third book, THE TITAN'S CURSE, being my favorite. Riordan may not have Rowling's great descriptive style, but he HAS provided a good storyline and some memorable characters.