The game was very enjoyable! The art and music were fantastic, the fact that the music was synced with the countdown was surprising!
My main gripe is something that other people have shared, which is that the countdown, while neat in concept, was useless in practice, since enemies would be able to get to you from any place in the room because the countdown was too generous.
Also, I think that damage could be better telegraphed. For instance one would think that an area marked in more intense red would be more powerful and deal more damage, but the diagonal attack, even if marked in a dimmer tone, was always stronger.
As for balancing, I think that enemies should scale between floors rather than between rooms. Yes, this would incentivize players to stay in a floor for as long as possible to grind for upgrades, but that can be mended through other means, such as scaling the power between floors relative to the number of upgrades received, so the sooner I move to the next floor, the less powerful that floor will be. The reason why I suggest scaling between floors is because I, as a player, like to get a feel of how well I fare against enemies, and testing against an enemy group but then have the next be more powerful kind of breaks that feeling of discovery.
Anyway, just a suggestion, take it or leave it.
The game was a lot of fun!!