Very cool game! The art is really nice, and the music is very nice as well.
As some others said, it was kinda confusing having the countdown in the same place as the tower cost.
Also it would be nice to see what towers do when you get them by hovering on them or something, although there is the gallery in the tutorial.
I almost made it, I got to like 95% but then I got destroyed T_T
Super fun! Great job :)