This was really fun! Took a few tries, but I made it to the end.
Like someone else said - I think mouse controls would've worked much better for the building system. It was pretty tough trying to select what I wanted to place while warding off enemies, but it did eventually become quick and intuitive.
My only other criticism is that the enemy tower's projectiles' hitboxes didn't perfectly align with the visuals provided. It did feel like I was getting hit by nothing sometimes. On the bright side, this was mostly what encouraged me to play defense, which isn't a bad thing.
Nonetheless, this game was really fast-paced and responsive, and I love that :]