I would totally play this game! I've played similar titles- notably Bloons TD Battles, but I like how you go and expand upon some features that would add more uniqueness to it. I think building your own path especially adds a lot of strategy and the opportunity to synergize your map style with your towers.
One thing I think would help your GDD is the clarity in some areas, and some spin or main focus for the game. I suggest more unique tower upgrades as a way to make it closer to a deck-building game, where the players could come up with really unique playstyles, even when using the same units. Another idea is really focusing on the map-making area of the game. That was really new and intriguing to me, and I think could be expanded upon more rather than the unit system.
I'd play sooo much of this game! Looking good.