Apart from its obvious capitalizing on the whole HP franchise and the market's desire for young-teen lit, it was a pretty good effort. I don't feel compelled to read any further adventures, except maybe to my daughter in a few years, but I have heard that there is now a movie in the works and I think that will be actually very fun. The "updating" of the Gods will work better in a movie than it did in the book, where sometimes a mythical character felt a bit forced or a tad obvious.
But for a simply excellent children's book about the Greek Gods, my money is still on D'Aulaires' Book of Greek Myths. And for when the kid gets a little older, The King Must Die by Mary Renault is an excellent portrayal of the Theseus myth, told in real, human terms.