Neat game, but a lot of the levels are way too short. The idea of the split path on level "3" (why does it start at 0? I know computers do, but the player isn't a computer) is neat, but said gimmick literally didn't even matter because there were only enough waves for me to build half the path. Level 4 was too short for me to finish the path as well, but I didn't even get to upgrade from the basic mushrooms before it was over! This kind of made the final level disappointing as well, as I was excited to try to find the most efficient setup, but it ended when half of my towers were still walls, and my setup probably would've been more efficient if I just didn't try to use the other half of the map at all.
The control scheme is kind of awkward as well. Middle click is annoying to pan the camera with, and replacing mushrooms is a bit tedious when you have to remove it, then pick the new one you want, and then place down the new one. It would have been nice if I could just place new mushrooms over old ones, for example. Camera panning could've probably been moved to right click, with a quick right click on a mushroom deleting it, but holding and dragging would pan.
Besides the minor stuff brought up in my feedback, this is a decently enjoyable game for as long as it lasts. I do agree with the other comments that something like a level editor could've probably quadrupled its longevity (or more!), but I don't regret installing it.