Nice game! One thing you can add is to have an upgrade system of some time so that there is  a sense of progression.

This was a cool one, you can try to make the enemies spawn faster with some more randomness to the health-packs too. Would love to play again if you are planning on polishing it.

Really fun game loop.

Typing master go brrrrrrrrrr!

this doesnt really require you to type "fast".  the difficulty is more or less how good you can spell if u type fast. trivializing the tower defense aspect of the game.