The resemblance to the old dos games made for CGA is very strong. I like that aspect. That said, it's hard to tell the archers apart from the footmen. I tried buying archers at first and only a while later realized I had mostly footmen.
I don't know if you would have enough time or desire left to fix it in time, but the in-game mouse cursor couldn't cover the full range of the screen, even despite the system mouse cursor clearly having more range. It looked like the mouse movement was being scaled in a way that didn't match the actual resolution the game ended up in. This didn't cause a problem playing the game, but I did have to restart the game to leave the instruction menu.
Also, it looked like there was a clear first wave, but after that the enemies just seem to trickle in constantly. I have limited experience with tower defense games myself, but in pretty much all games with huge amounts of enemies and in-game currency to spend tend toward discrete waves and rest periods so that the player doesn't need to juggle ui elements with combat.