I like the little character models.
A simple tweak I think would have helped would be having a description of what each of the plant does. I had to throw a few rounds just experimenting to see what each plant does.
It's also a bit awkward that if you have exactly 30 health, you can buy a 30-cost plant and then immediately die.
In the end, I put cacti on every corner where they would hit a bunch of road and that was enough to win. The cactus may be a little overpowered.
Would have liked to have some SFX and music.
Spending your health as the resource to build was an interesting experiment to try, but I'm not sure it work out for the best, since in a game like this, if your base starts taking damage, you've basically lost either way, so there was no incentive to actually save up blood.
Fun tower defense, though!