Amazingly fun for such a simple concept, I would look at the range on the cells, perhaps they should be leashed if the enemy gets outside a certain range (I had some chase enemies right off the screen. This also could be a function of the scaling, it didn't work overly well for meit was really hard to read some information and see some of the UI. I love the randomized upgrade trees, but I did find the ranged cells were a bit OP compared to the attempts when I didn't get them.
Love it overall and can't wait to see more.