Fairly solid but nothing terribly origional.
Not being able to move at angles was a bit of a pain.
There should enough lag between the last enemy in the wave and the upgrade screen that you can at least try to get the upgrades that are dropped on the battlefield.
Pink tanks aren't very intimidating by the way xD
As far as play mechanics it seemed pretty solid, it doesn't take long before you're ungodly powerful though.
I really dug the accuracy and the "by the skin of your teeth" bonuses. Nice touch.