This game was exciting, definitely the game I played for the longest so far, with just sheer, "how can I get further". With that said I was able to reach wave 20. The enemies were well thought out and I enjoyed all of the mechanics, minus boost (I might not be dexterous enough to effectively use it) and armor (already pointed out). The art, audio, controls, and shop system are all pretty top notch for 72 hours of development.
With that said, a couple points of feedback. The currency didn't always visually pickup, loved the sound it made though. This was a small bug and didn't really get in the way of gameplay. From a balancing perspective, after wave 12-ish the scaling of everything costing more in the shop mixed with the oppressive amount of arena shrinkage gets to the point where you are forced into repairing and increasing arena size to progress, without even looking at potential other upgrades. Not that it fully matters if you get a lucky start, you can one shot all enemies for the rest of the game if you get enough damage ups early on. Scaling enemy strength/health rather than just number spawned on later levels could be an interesting avenue. I would like to see armor implemented in an impactful way so that you can scale the cost of repairing based on how much armor you have, and have it so that repairing doesn't arbitrarily jump in cost every few waves like the upgrades and room space. Then it would be possible to weigh forgoing health for that juicy upgrade. In addition it felt like the currency gain curve fell off with the exponential style growth of room size cost doubling and also shrinking by a larger factor every round.
In all, these are my opinions, slightly nit-picky because this game already feels so polished and I enjoyed playing it a great deal.
AMAZING game for the Jam. I had a lot of fun and would be stoked to play an updated version!