Just changed rating from 4 to 3, tired of the stupid outside area raids (which miraculously only occur after you discover the outside areas!); plus this gets really repetitively boring after a while. Needs some survivors to rescue, unique things to explore (subway train? department store?), etc.
Does anyone even use the order / history box on the side? I think it could be eliminated without sacrificing a single aspect of game play. (I say this as someone who's gotten gold on levels 1, 2, 3 and Europe, and beaten Crazy in 46, all without ever using the history box).
Try to sell some upgrades, that chain reaction will not be so fast, and as result you will get some few additional clicks :)