Awesome game. I had a blast nailing down waves of enemies.
The first waves give you the feeling that you're in control, but once you are around Wave 10 then you feel you're in a rampage where I just felt I was dieing slowly without a tactical way to survive. I basically kept moving away from the enemies to be out of their range and let the overheating go down. (Not sure if I played the updated version as it didn't seem like my shield was restoring after a wave, but I did just download it)
It would be nice if you could also move up and down and/or have the possibility to shield yourself behind the wreckage of a chopper or a bike. And maybe have a block here and there that allow you to think tactically instead of only trying to stay out of range from the enemies.