Made it to wave 25! It's a surprisingly well-balanced experience, with an equally surprising amount of depth to the upgrade choices and possible builds. I would have liked the early game to have some more variety, maybe starting with some money or having cheaper starting upgrades so you can get started on upgrading right away rather than after room 3 or so.
I also noticed a few of minor issues, nothing that hindered gameplay though. Those issues were:
1. Sometimes the bone-chuckers would just not chuck bones? Seemed to be in certain rooms, I think pretty consistently in the top left room they would just kinda walk around.
2. The center room seemed to not have a shop? Made me think it was a chance thing for each room to have a shop but no, that seems to be the only one without it.
3. The wall at the bottom of each room, while looking cool and adding some legitimacy to the space, would often cover up enemies. I found myself walking into that blocked area sometimes and would run into an unseen enemy, which didn't feel great. You may make the perspective sort of even more top down, like The Binding of Isaac.
Ultimately, I really enjoyed this game! I could see this expanded with more weapon upgrades, enemy varieties, and perhaps a more involved story or some kind of end game.