As a guess, I'd say that swapping Travis Taylor with Stephanie Osborne as co-author was not the best choice. It seems common enough that sequels don't measure up to the first in a series, but the drop-off from Human By Choice is rather more abrupt than most. The characters in The Y Factor are one-dimensional and the plot has gaps that are disconcerting.
From the beginning, the reader is asked to believe that "Miss" Trung is a 29 year old senior scientist with two PhDs and a history that includes a stint in the US Army. Her life prior to the opening chapter is never explained in any detail but fitting in an undergraduate degree, two PhDs, one in molecular microbiology, a couple of years in the Army, and enough research work to be heading up a research group and a priority acquisition by a super secret government agency into 29 years is stretching the limits of believability. Unfortunately, that's just the first of many unbelievable or at least unsupported story elements.
Another jarring note is the authors' heavy handed anti-Islamic bias, although the treatment of the Hindu religion isn't much better. Again, this ties in the rather black and white, good or bad, treatment of the various characters.
Oh, and if by some chance you're looking for romantic or possibly erotic fiction, the rating would be ZZZZZ. Five Zs for a real sleeper.
I gave it two stars instead of one only because I actually was able to finish it. But it was a close thing. Avoid this one.