It becomes way to easy after a certain point, especially so because damage gets to a point that all enemies die by one bullet, and you fire fast enough to hit all enemies in a second or two, I easily hit wave one hundred and twenty, if I may suggest, add in a point where enemies get tougher, probably fifteen waves after the last enemy shows up, and maybe fix the upgrade system, tapping the plus every time is difficult on a chrome book, also fast forward multiplies the speed by well over three, it should only be two, maybe add in three different speed settings.