Nice! A suggestion for Kongregate: add an achievement for getting all the gold stars for the levels. Just completing them is fun, but it takes some effort to get the golds! How about some incentive here? Plus this up if you agree. :D
Overall a good concept, but I have to agree with the earlier post about the fact that the Antimatter Shield and the Sticky Shield both use the mouse button. Too often I am trying to catch and fire things back at the tanks, and after buying the Antimatter Shield, it destroys most of the missles I am trying to catch. Take the mouse button and use it for the Sticky Shield, and only use the space bar for the Antimatter Shield.
I have tried to play the game several times. The main bug that causes the screen to blank out in sections (leaving invisible people and offices, although you can usually see their emoticon balloons) seems to occur when an elevator is upgraded all the way, or when a third car is added to one elevator. I got around this by only upgrading the elevator once, only using two cars, and replacing it with a lift tube as soon as possible. That way I got all of the objectives done in the game. The only problem I had then is that the game didn't save my tower so I could finish it completely. :(
 "Flaming Zombooka 3 : Carnival"){kind=icon}
 "Shield Defense"){kind=icon}
 "Corporation Inc."){kind=icon}
 "Little Wheel"){kind=icon}