I have read every single one of James Rollins' books. I think he's a genius writer, and have enjoyed them all. I particularly loved Sandstorm, Amazonia and Ice Hunt.
However, when reading his other books, I've been hooked into the plot line virtually from the first page. With this one, it took me several reading sessions before that happened. I think that's probably due to the jumping around of time and place in the first several chapters, which left me a little confused and unable to keep up for a while.
Also, he's left us with two major cliffhangers, and an open ending that I don't think he'll ever complete -- something he hasn't done in previous books which have been "stand alone" products. It makes the book seem more like a chapter in a broader plot line, rather than a great novel in its own right. I just hope he continues to develop the characters and storyline further, while maintaining his thrilling writing standards and familiar recipe for page-turning entertainment.
Saying that, the book had Rollins' usual fast-paced (breakneck speed, actually!) adventure woven in with scientific fact and fiction, as well as the characters we know and love from SIGMA. I love the way he manages to do this in a way that, although far-fetched, could be just about believable with a generous stretch of the imagination.
To sum things up, I would still recommend this to fans of Rollins and other science-fiction/thriller/adventure books. It'll certainly get you thinking -- of both past and future -- if nothing else.