Let's see. First, people with not average/old computers get fucked up by this game because there isn't a graphic quality button, which is essential for any game.
Second, what's up with the difficulty ramp of the game? First level is piece of cake then second level is hard as fuck? I mean, the robots, even the huge ones drop 2, I repeat, TWO fucking scrap pieces, which makes no sense. That makes a lot hard to upgrade your stuff, build towers and the medi station.
Also, IF you are going those 2 issues, make the time between wave incomes bigger. First wave comes 20-30 robots, 5 seconds later, comes another wave while you haven't even cleared the first wave. Now THAT is gamebreaking.
I'm pretty sure that this game will get a lot of better scores if you fix those issue.