That's a great implementation of a short tower defense; it's fun to see the towers/plants growing every night.
I think that, in terms of game design, there is an issue that there are no incentives for the players to plant anywhere other than at the beginning of the road. Usually, tower defense games fix that by using limited space, and/or multiple lines of enemies.
The sprites and the sounds have a great fit together. I really like how chill the game feels.