Don't get me wrong, I am happy to see another side of Rick Riordan's world, and I enjoyed the read. 
 The formula is the same as the two other series, and I guess as an introduction to the world, it would be great but to me, it did feel a little bit redundant, even if still nice. 
 Also, I just love "crossovers" in general and even not being that a fan of Annabeth, just having her there in the far far background but not involved at all felt weird and I was disappointed. I think I'd rather not have her at all, without the baiting that felt way to much like fan pleasing. 
 The book has lots of references that also appeal to the fan base. 
 I am a little bit disappointed how repetitive the characters and settings and plots seemed to be. I'd still read the rest though, maybe even pre-order The Hammer of Thor just because ;)