Ever since the family finally convinced my sister into reading Harry Potter, I should have known that there would be a price to pay. The cost ended up being Percy Jackson, a young readers series by Rick Riordan that could be described short-hand as Harry Potter mixed with Greek mythology.
I began reading Harry in 1999, when I was just entering college, so it's safe to say that generally speaking, I wasn't among the immediate target audience, though as many other readers (the author among them) discovered J.K. Rowling wasn't just writing for kids, and her books were all the better for it. Publishers, however, quickly realized that they could release a slew of similar adventures aimed directly at the young readers market, from writers who did not necessarily share Rowling's talent. Anyone older than middle school quickly learned that it was a dicey game to navigate these waters. I myself sampled the excellent Series of Unfortunate Events, as well as Dave Barry and Ridley Pearson's Peter Pan tales (otherwise known as the Starcatcher series), but stayed away from the others, suspecting that they wouldn't be of literary interest to me. Hollywood displayed no such qualms, however, but soon learned that you can't just assume there's a mass audience for everything.
Anyway, the young readers genre eventually shifted ages slightly, which led to a flood of books that eventually gave us the Twilight Saga and the Hunger Games books (I haven't read any of the former, and most of the latter, which could have used so judicious editorial notes), as well as the first of James Patterson's Witch and Wizard series. Given that many male readers gravitate toward mystery or fantasy material, and that many female readers gravitate toward romance, it's no wonder that the older the reader is expected to be, the more blended the typical adventure narratives become with these impulses.
Riordan comes from a adults mystery background, but at least at the level of his Percy Jackson books writes about to the competency of Patterson when he's directing his material at young readers. I had avoided his books because I feared that they were pale imitations of Harry Potter, and because I'm fairly familiar with Greek mythology, and didn't care to see someone bastardize it for the sake of convenience. The actual results as featured in The Lightning Thief are somewhere between inspired and labored. In more capable hands, the same material would be worthy of Riordan's ambitions, to write a modern heroic saga in the tradition of Hercules and other Greek legends. Riordan, however, can't get into the heads of his own protagonists, which is something of a problem. For less discriminating readers, it's no doubt engaging material, but there's no reason, as Rowling demonstrated, that a writer must cop to one audience, or compromise the style. Good writing will always out. Riordan's words, at least in this one book, is not good writing, competent yes, but then, who decided that competent writing was good enough? Inspiration counts at least for half, and Riordan has half the amount of inspiration he needed to make it work. Without Harry Potter, there would have been no Percy Jackson, and that's a damning kind of judgment to level on anything.
Still, it's salvageable, as I suggested, and entertaining enough so that you should not feel embarrassed to read it, or suggest it to a reluctant reader. If it encourages them to discover more about Greek myth, or to use those myths to better use themselves, then all the better. Sometimes that's as much as you can ask from something like this.