The worst thing that can happen to a book series such as the Sigma force series is to become predictable, and I'm afraid these books are starting to become predictable, especially the action scenes.
Don't get me wrong the overall plots are top-notch unbelievable, but the individual "fight scenes" are getting rather too predictable, because nobody major dies. These books are becoming very structured and formulaic. A character gets in a perilous situation, situation grows worse, then at the last minute, they escape and survive. Sure some background characters die, but who cares about them anyway? I'm starting to just flip through the action scenes because they really don't matter. They are just placed there as a forced means to create intensity.
Now I love all the characters; I think they are all interesting in their own right, but killing just one, really ups the ante in these "fight scenes" and can really bring back that initial spark that the first couple of books in the series had. (the spark died out when Rollins brought back Monk because it revealed he didn't have it in him to kill off a major character)