I have to admit that I didn't like "Alien proliferation" as much as the other three books. Don't get me wrong, it is still an excellent read, but while I thought that first three books in the series were flawless, I could pinpoint some minor minuses in this one. 
 The first quarter of the book was kind of slow because of Kitty's pregnancy. But what upseted me the most was that Kitty wasn't her sharp self. I love this heroine because of her brain, because she gets everything better and faster than any other character. But pregnancy made her slow, forgetful and needy. Happily, our Kitty is back in the second half of the book where we can see her cracking megalomaniac plans and figuring out all conspiracy theories. 
 By the way, this book wasn't much on the action like the others were. In "Alien proliferation" instead of fights with superbeings they try to solve conspiracy theories. A lot of them. Actually my head started to hurt trying to understand what's going on, who is a mole (or if the even have one) and who the bad and the good guys are. 
 There were some more minor flaws and because of them my actual rating for this one is 4.5 stars 
 But I still loved this book. I still love Kitty's humor, her new partner, poofies, the Density Twins, Martini's jealousy, ACE worship of Kitty, Reader's cover-boy grin and a lot of other things.