This is similar to what I was trying to do with my game. Were you at all inspired by Gungeon?  I have a couple issues  though, the floor 1 boss won't die, the powerups didn't really help and I ended up avoiding them more than I did collect them. Please give the enemies hp bars I felt totally useless pelting the boss with the hundredth bullet for him to keep living and spawning more skeletons. I was really determined to see floor 2 but I gave up because the game was way too tough. My main frustration was the reloading, it's all great and immersive but without health potions and aggressive enemies going Mach 10, it was hard to have fun. I probably played for 4 hours. I can say definitively, it needs a bit of work. I feel like it was way way too hard. However, it its an awesome concept and I really think that had it been a slightly more balanced for the player I would have enjoyed much more. Halfway through writing this I went back extra determined to get to floor 2 and I did, and even got to floor 3. Btw I do like the transition area I think that's a really nice touch. All in all, you've definitely got a good idea.

Oh and I should definitely mention that there's a hole in your collision layer for the player.

i feel like the powerups providing a downside feels a bit overkill- the enemies are already quite aggressive and tying enemy upgrades to the levels might feel more natural