It's a fun little game, there seems to be a problem with challenge though. There is a ton of content for higher difficulty levels (better units to use), but the game doesn't really get harder fast enough!
Hmp. Not fun to have a lag spike every few seconds. I can imagine that the dev expects us to have system of a certain power level, but a bit of optimization doesn't hurt. Very good game!
A bit of optimization is definitely needed and will be done soon :)