Upon second viewing, I'm lowering my rating. I still found the first hour engaging, but, once the action moves to a pedestrian-free, trafficless Rome, the film as a whole jumps off a cliff (pun intended). The action setpieces become increasingly ridiculous, the story devolves into a series of flip-flops and reversals, and the number of times one of the characters pontificates about "The Key" is comical.
Overall, a huge let-down from the previous installment.