Cool game, I would love to see it get fleshed out even further. Maybe enemy units could start getting stronger when you get some number of waves in and then maybe there could be a way to research player unit upgrades. I got up to somewhere past wave 35 and at that point the enemy ground units were irrelevant and I was mostly just rebuilding what the jets destroyed and expanding the base. It would be nice if there were buttons to build like 10 units or something instead of just 1 at a time. Also, there should be shortcut keys to build/place units.