Cool, sounds like you got a good idea of what progress to make. Here's a couple clarifications and thoughts on things you said:
Hard to read interactables has been a common complaint, I'll eventually try to do something about it, perhaps play with color coding more, I've been using a limited 64 colors palette
Maybe use a toggleable outline shader for all interactables? Or some other finder thing. Though that may look messy given the pixel art. Guess that's a bit of a bandaid fix.
I'm aware there is an ammo balancing issue
You probably wrote this as you read, but to be clear, this statement of low ammo was spurred by the confusion of the ammo display. After I figured it out, it seemed fine. Though, I did use the pistol for most of the way to Rumia.
I didn't really want the teleporters to be jarringly fast, you could say the animation is for "flavor" rather than any other gameplay reasons, enemies are supposed to come out of the teleporters when alarms sound and the animation will be helpful in being able to react as they come
I think the animation is fine, it's just a little long when you want to quickly go between rooms. Or, one time I accidentally got sucked into the walking-towards-telepad animation when walking near. As for enemies, you can just have the walk-to animation be for them in all instances. And, the player only for cinematic parts like the start and end of the level. But, it isn't that bad as is. I just have a certain taste for minimizing cutscenes(no control) in gameplay.
I've been noticing the dullness myself lately even while playtesting, I have things in mind to spice it up like enemies spawning out of screen as reinforcements, more traps, puzzles, etc. In the roguelite mode I noticed it gets more interesting when there are more than two enemies shooting at you, going through a map definitely shouldn't feel like an empty walk through a park.
Some other ideas could be, locking the room behind you until you kill all the enemies; so you don't take pot shots from the hallway, or enemies that spot you will notify other enemies in their own line of sight. Though, idk how hard that would be when you have the alarm system. But I don't think I ever saw an enemy cause it, only cameras.
You fell victim to me not properly pointing out that the fridges could be used to set checkpoints, that's another thing I plan to improve in the future.
I did find that out, and I was a bit surprised. So that wasn't the problem, I died once to Rumia, I think once more in the 2nd half, then a 3rd when walking into that acid. idk if me having to restart the level at that point was intended.
Also I don't think you found any secrets, perhaps I hid them way too well, I'm thinking I should have the AI companion at least try to point out the first one for free in order to train the player to look for them.
I did find a duct behind a crate near the (first?)blue keycard locked area. I went back there after getting the key, and it had some goodies and a shotgun I think, but its spread was so big that I opted not to use it.
Also a bug I forgot to mention. I got to the yellow keycard area, and I tried to open the door without the key several times. Later I returned with the key, but surprisingly the door was already opened. Did it remember me trying to open earlier, and auto open after collecting the key? Kind of odd.
Thank you for all the feedback! It helping me refining my ideas a lot!
Glad it's of use.