James Rollins has penned a number of excellent escapist novels. I would recommend Ice Hunt, Subterranean, Amazonia and Sandstorm to anyone who enjoys adventuring science/techno-thrillers. I would be more reluctant to do so with The Doomsday Key, though.
This is yet another thoroughly researched, keep-surviving-by-the-skin-of-your-teeth adventure. Less pronounced in this book yet still present is Rollins' tendency to move from cliffhanger to cliffhanger, with small breathers in between. It is a book to enjoy during a flight or a rainy weekend - and it will keep you turning pages for hours. However, for a number of reasons this would had been a much better book had it not been yet another Sigma sequel.
Sigma simply does not work that good for me. I cannot buy the small number of people undertaking such critical tasks. In fact, Sigma is so understaffed that not only has to rely on certified idiots (sorry Kowalski, but you know it is true...) but even the director himself has to go into the field. They operate all over the world under thin pretexts, they do not even seem to be official sanctioned. And to add insult to injury, most new recruits seem to suffer the Star Trek's away-party odd crew-member fate...
On top of that, Sigma seems to deal with one crisis after another while under attack from both a shadow power group and other government secret services. For a writer who takes great pride in the accuracy of his facts interweaved with his fiction, this requires a continuous leap of faith.
I can understand how having a book franchise can work for both the writer and his publisher. The first has a set framework of characters to weave his new plot with whereas the later has a more or less loyal fun-base to fall back to. However, they should both keep in mind that this does not always work for the reader.