I liked the game and the minimalist aesthetic is a good fit!
I think the biggest room for improvement is in the realm of UX. You see the player leveling up after every wave, but there's no real way to keep track of what the players stats currently are. Ideally I would know which 'build' the player is going for and then have a choice to react to that via different unit prioritization.
So yeah! Promising concept, could do well with an additional design pass and some added units. :)