Several things here:
1.The difficulty ramp is way too steep. Making your game longer by making players grind is incredibly annoying and lazy.
2.Shielded bloons are overpowered. There are several stages early on where you get swarmed by shielded bloons and lose control of the super monkey. The research idea for the shielded bloons is good, but the rate increase per level isn't near enough to match the speed of the game.
3. Purchasing money. I understand wanting to make a profit from your game, but this is ridiculous. The most expensive package only pays for maybe one or two major upgrades. Charging that much for so little is a surefire way to lose players. Why does every ninjakiwi game have a purchase option on it? A bit greedy if you ask me.
 "Bloons Super Monkey 2"){kind=icon}
 "CrossFire Madness"){kind=icon}
 "Llama in your Face"){kind=icon}
 "Coinbox Hero"){kind=icon}