Good game, but...
Difficulty scales up far too fast. You have to play the first level several times to get enough upgrades to really beat the other ones at a moderate pace instead of a frenzied, nearly dying pace.
All in all, however, great game!
Also, FryGuyCrate, if that were the case, then the game would skip to level 111 after level 11. It's called Roman Numberals. I = 1, II=2, III=3, IV=4, etc.