Love the game. Although it is a little bit taxing for the computer to run it. I find myself beating this like I beat most NES mario games, flying over the entire level haha
The last level is beatable 100%. I have done it myself (at least on normal mode) You need 2 upgraded plasma bombs to the max on the outside 2 weapon slots, and in the middle you need homing missiles. Don't be afraid to crash in to a few enemies because that is the secret. Save your bomb for when you need it MOST.
It is essential to have the Banana farm towers. They give you tons of cash. Even though it doesn't seem like it at first, they are a game changer when you get in to free play mode.
I don't like how in the new hero battles my heroes automatically move. I cannot strategically place them at all without them ending way spread out on the battlefield.