This is the best I managed, the super big enemy could take a beating and dish one out!
A good, fun game in general. I feel the prices for upgrades were highly priced, often too out of reach. Ideally the player should be able to purchase something at the end of the very first wave, otherwise there's no agency to be had when the fort takes damage on Wave 2. It gives the sense that nothing could be done, whereas if two or more upgrades are affordable and the fort takes damage, the player can think "Oh, I should have tried something different."
The randomization of the waves helps add variety and in theory makes for better replayability, but this also means that the amount of gold the player earns is random as well in a way they can't control. On my first playthrough I could only afford a speed upgrade after Wave 2, and on my second playthrough I could instead buy the much more useful 2xDamage upgrade instead, simply because more enemies spawned for me that run.