This is an amazing book!! It's also surprisingly educational as well because as someone who just finished up this series I can honestly say that I have learned more about Greek mythology from this series than any teacher who has ever taught me. So that's a thumbs up. Now let's get down to business:
Violence: Yes, this book is all about a war but it is actually very un-violent, especially when you consider that the only weapons they have are swords and daggers. *SPOILERS* even when Annabeth got stabbed halfway through there's only a sentence about her crumpling to the ground and the blood starting to soak through her shirt, not that much considering that she got STABBED. So overall violence isn't that much of a big deal.
Sex: *SPOILERS* Percy and Annabeth kiss at the end, which is nothing considering how their 16 years old and how most teenagers take it a lot further. So overall sex isn't a big deal.
Foul Language: The worst there is is when Percy says the word "sucks", which again is not that bad considering that he's 15/16 years old and most teens say a lot worse these days. So overall foul language is not that bad.
Product Placement: Yes, there is a lot of mention of brand names, but it's said in a non-advertising way. So overall, depending on how you look at it, product placement isn't that bad.
Drinking, Smoking, and Drugs: Yes, Dionysus is the god of wine but they don't mention it nearly as much as in the other books. There's no drug use and nobody smokes. So overall the D,S, and D's aren't a problem.
Bad Messages: As far as I can remember there aren't any bad messages, in fact any messages this book teaches is how loyalty to friends pays off in the end. So overall bad messages aren't a problem
Bad Role Models: Yes, there are bad people such as Kronos in the book who want to harm others, but they're always portrayed in a bad light, whereas those who want to save Mt. Olympus are always portrayed in a good light. So overall bad role models aren't a problem.
So in conclusion this is one of the best books I have ever read. I definitely recommend this book to anyone who wants to read a great story while learning a few things in the process.