Sniper Hut probably needs to be looked at. The early game is super unforgiving. Then as soon as you get a single Sniper Hut, looking at a 5-10 tile long straight, it's over. It outscales the HP scaling of the enemies and it makes everything that hits that straight die, effectively regardless of speed. I'm currently on Wave 81 and see no possible way I could really lose from here, unless the scaling goes absolutely wild out of nowhere.
Also badly needs a speedup button. Waves get so long after a while.