Tennesse to Las Vegas in less then a day in an old truck? Nope. How did they pay for gas? Las Vegas to Hollywood in 2 hours? Without a speeding ticket? Much less traffic going through LA? With all of the other kids, why suspect Percy? Just because he was Poseidons son? Was there something else? Then, let's consider the sword play. I don't expect Hollywood to do realistic sword play, but what they had... Sheesh. Horrorific. If Percy is hardwired to know how to use a sword, why train? If they are all Demi-Gods and have at least some of their parents power, why weren't they training to use those in a fight? Why train with swords and armor in the modern world anyway?
The bad: Plot was tired scientist vs evil corp/military types. Done better most in that style, but still predictable.
The good: At least the guy leading the forces of good was an actual military guy, and a marine instead of some scientist who knows nothing about fighting.
The spectacular: A completley alien world, outdoors with very alien looking creatures and plants.
Way too many holes in the story. Too much jumping around. First she's underwater with what's her name coming after her, then next she's on the beach. First she's in italy, then she's back. The CGI on the werewolves was good. If Bella is immune to vampire powers, why can what's her name see her in her vision? Won't be seeing the final one.