Played a lot more and all of the basic systems seem good. I can get a few levels in on a run on easy mode, not that far in normal. I think perhaps the difficulty early game could be adjusted a bit if this is going the roguelite direction in the end, make sure the first few levels are always pretty simple by keeping the amount of spawning enemies limited.
Gamefeel is good, though I still think a slowdown while you change your chemical set up would be a vast improvement. Would it be abusable? Yes, but I do not think that would be a problem, I think it would enhance how the gameplay feels. I would try it, put out a test-build and see how people respond to it.
I still need to put in more time in this, more thoughts may come.
Both of the enemies in this work well and are easy to understand. I think maybe adding a "filler enemy" something, more or less not that dangerous and slow could be good to fill out early rooms before ramping up the difficulty. Otherwise: stationary turret enemies, enemies that change their chemical setup,
I want a rifle-version of the gun.