It's fortunate that the damage ramps so slowly, because cash accumulates at a maddeningly slow rate, making planting a large number of towers impossible, and upgrading one tower even worse.
Whenever I play a PETA game, I wonder just whether or not they're even really trying to get their point across. The Cooking Mama parody they did actually made me want to go cook something.
When you have to assert that your third level is in fact possible more than once in the level itself, chances are you've gotten a little too carried away with the difficulty.
It seems like you ran out of ideas to try to improve the boring combat, so 3/4 of the way through the game you just decide to rape the player with an enemy who can infinite combo... what the hell?
Once you've bought everything, the last wave is just... tedious. I mean, you've got an eternity just sitting there doing the same things over and over until your inevitable victory. Prior to buying everything, though, the difficulty is insane. There is no balance between the two. Anywhere.
 "Walker moves around"){kind=icon}
 "I Love Traffic"){kind=icon}
 "Kayadans: Bugs Tower Defense"){kind=icon}
 "Bloody Burberry: The Fur Fighters"){kind=icon}
 "Crush the Castle"){kind=icon}
 "GermChain"){kind=icon}
 "The Most Boring Game Ever!"){kind=icon}
 "Sacred Seasons MMORPG"){kind=icon}
 "Desert Samurai"){kind=icon}
 "Mouse Maze Galore"){kind=icon}
 "Red Moon"){kind=icon}
 "Tree Of Life Tower Defense"){kind=icon}
 "The Great Siege"){kind=icon}