Interesting concept! The main problem I've encountered is that the rate of progression of your own power is never able to keep up with that of the tower, so you're essentially in a losing battle against the clock to even touch the tower- let alone destroy it.
Thanks for the feedback! You described exactly what I had in mind when creating the game. Since this was my first game, my main goal was simply to see whether I could make something at all. Because of that, things like balance and game design ended up taking a back seat.
By the time I realized it, it was already too late to change much :(
So I balanced the game in a way that lets the player make it to the end and eventually overwhelm the tower with a massive zombie horde.
Anyway, I really hope you still enjoyed the game!