The first thing to point out is that this reads very much like YA, but doesn't seem to be marketed as such. That had me a little off-balance. To me, it's a YA version of the Da Vinci Code that's had Christianity extracted and Atlantis added. There's a generous sprinkling of Indiana Jones thrown in, and the whole thing has been left to simmer, before being lightly seasoned with Clive Cussler to serve.
It's a fun read. Kind of like a Blockbuster film, you need to be fully prepared to suspend your disbelief for a few hours and just let yourself be entertained. There's a hot teenage lead with a body 'like a Greek God', an attractive, fearless female sidekick, a secret, ruthless government agency, a mad professor, vague prophecies, High Priests, a secret Nazi facility, a bloody big sea serpent, magic crystals and, best of all, an all night Zombie film fest.
If you're looking for anything meaningful or emotional, this isn't what you're after. If you just want to have some fun with a hot lad with gills and a lot of helicopter action, this is just the ticket. It's fast-paced and instantly engaging, and has an ending which sets up book two beautifully.
For me, it lost some of its appeal in the later stages. I found Erebos' mass Atlantean info-dump to be a bit clumsy, and I got frustrated with the number of times the 'do what we say or the girl gets it' get-out was used. But on the whole, it was enjoyable, much more so than I would've thought!
A great read for teenage lads I'd imagine, lots of video-game style action to enjoy.