I don't know if the game was updated since people had reviewed that it was too hard (I kind of doubt it since the game is still off center), but I did not find it to be hard at all. On the contrary, I felt the balance was tipped a bit too much in my favor. Perhaps it was because more difficult enemies never appeared. I quit playing at wave 36 because nothing changed.
For those who don't understand the upgrades the first one seems to be shot power (it is slow, but eventually you get one hit kills), the second is shot speed (kinda useless), and the third is the number of shots (very useful especially in the beginning). Hold down the mouse button and point at the baddies. I never lost a tree.
That being said I wonder if they really are baddies. I mean biohazard suits to cut down trees?? Me thinks they are there to stop an alien/ mutant tree invasion. Granted these beasts bestow crazy powers to those willing to follow them, but what kind of end do they really seek.. And where do the bodies go? Are they eating them? I think they are. Crazy smiling trees all happy and innocent looking feasting on the flesh of their enemies, and you their pseudo-symbiotic zombie defender imbued with the power to shoot exploding flowers from your hands.. if you can even still call them your hands. The root tendrils that twist through your body up your spinal column and across your brain. down your limbs to your very extremities, exposed they force you to become the weapon of the trees.. dastardly.
Good job. I liked it. You should fix the centering of the game, add advanced enemies, and some more fun upgrades. And an end.. how long does this go on anyhow?