Cool game! I like how you used the concept of a reverse tower defence - it sort of turns it more into a management game as you try and keep everyone's health up. One pretty major issue, though, is that the screen didn't scale for me - I could see most of the course, but the far left and right were cut off, and I couldn't see money either, which was a slight problem. The game was still playable, thankfully. Some variety in towers would've helped make the game more interesting too, and the waves could've been a bit shorter, since I was just sat there with my 4 towers on wave 1 doing nothing but watching the same enemies go by and get healed.
I do love the graphics of this game, though! The squigglevision on the towers was a great touch, and the enemies (Are they enemies if we heal them?) were nice looking too, although I think it would've looked even better if they didn't have anti-aliasing between the spots. I like how the UI (or what I could see of it) fit into the style of the game too. The music fit the feel of the game, and the sound effects were decent too, although some variance in them would've helped make them feel a bit less repetitive.
I really liked this game, though! It's a great concept, and if you choose to continue developing it, it's got great potential too! Great work!