Lots of Lag.
I don't think it's possible to lose this game. I let one guy swing back and forth until he was so huge he covered most of the screen. 300 levels is way too much, I got up to level 100 and there were so many bad guys that it lagged my computer down to a crawl and each click killed 5 to 10 of them. I can't imagine what level 300 would be like.