On my first playthrough, I was quickly swarmed by enemies and lost. The second playthrough, I made sure to construct a combat warden I had designed (two laser guns and max armor) and systematically took out all nearby hives that were threatening my units or close to crystals, which took a while.
I beat the level without having ever used walls or towers, as it wasn't clear to me what their purpose was. I experimented with them afterwards, and could see how they would've been useful.
The game loop is solid, overall. The more units you build, the harder it is to switch between them. I wish there was a mini map where I pick individual units, or some ability to zoom out so I have a better view of my units. Because otherwise, it's hard to spread them out in different places.
The low poly art style is well done here, and I like the metallic sheen on my units. It seems enemy nests can only be damaged at certain points (maybe when enemies pop out of it?) so there should be some indicator for when they can be damaged. Maybe have them pop out of the ground for a bit?
I can't think of many directions to take the game from here off the top of my head, but the foundation is already good, so the sky is the limit.