Finally finished this one. It took a long time to read - not because it was badly written, but just because I've had a lot of other things on my plate.
I actually enjoyed this more than the first two Alex Cross novels. There's still a lot of killing going on, but it didn't feel as gory and intense; it wasn't as emotionally draining as the other books, because the Jack and Jill killers are politically motivated, not motivated by sick, twisted psychology like Gary Soneji or Casanova.
Unlike the first two books, which were part mystery and part psychological thriller, this one is more a spy thriller. We know who's doing the killing. (We don't actually find out the identity of Jack till the end of the book, but we do know he and Jill are the ones doing the killing.) The book is less whodunit, and more can-they-be-caught-before-they-kill-again. A couple of really good plot twists at the end of the book, too.
The Jack-and-Jill storyline alternates with another story where there's a person killing kids at Cross's son's school. This storyline is a lot more like those in the first two Cross books - the creepy psychological aspect of the murders, the gory details. Either of these plot lines could have been enough to base the entire novel on, but by having them in the same book, Patterson can show Cross's frustration at being pulled away from what matters more to him (the student murders, in his own backyard) to work on the more high profile case.