Author and blogger Brian Drake has written a really insightful review of Killer Instincts. One of Brian's main points in the review is that in KI, the story isn't about the showdown between William and the Paggiano family, the story is about William's transformation from aimless college kid to cold-hearted killer. In short, the journey is the destination here.
Of course, I think Brian says it a lot better than I can. Check out the review on his blog, Brian Drake at Large.