Just played the demo on Steam and I loved it! I have some feedback I'd like to give though that I hope you'll take to heart when finishing the game!
Better player feedback for slowing time: I think just slowing down time isn't enough in terms of feedback, and including something like a darkness effect on everything except the player and bullets or a particle effect would be nice.
Adjustments to slowing time: I thought it felt weird that instead of going straight to 50% time, first, time straight up stops, then speeds up to 50%. I think going straight to 50% or lerping from 100% to 50% would both be good options, but it kept throwing me off when time would just completely stop for a second.
Improvements to interacting with things: I realized that I could still interact with things even when I was facing away from them, which resulted in me accidentally interacting with a few things that I didn't mean to, which was annoying when it was a character with a lot of dialogue I had to skip through.
Better bullet colors: I thought the blue bullets were fine, but the green ones often blended into the background for me which made it hard to see them if I wasn't looking for them, and lots of times they would hit me out of nowhere. This was only a real problem in the hotel because of the color of the floor, but I think maybe adding an outline to the bullets or changing the color of the green one would be the best option. I like to do a "squint test" to see if colors work for my games, and if you can't see everything crucial while squinting, then that means you need to adjust your colors. A colorblind mode may also help because I'm a little colorblind which also may be while I was having troubles.
More feedback in general: I noticed there wasn't much feedback in most systems which made interacting with some things feel a little off and overall made the game feel a little unpolished. I noticed a lack of particles which I think would go a long way towards polishing some aspects of the game. I know this is a little vague, but it's more general feedback than specific.
Boss direction indicator toggle: I loved this feature as it made it so much easier to aim in the direction of the boss! However, I think some players may opt to turn it off for a little more challenge. I'm not sure if this is already part of the Masochist Mode or something cause I only played through the Intended Difficulty, but if not, it could also be a part of Masochist Mode.
Shadows/better depth perception: There were lots of times in the game where I was slightly confused about the depth of certain parts of the levels, and I think if there were shadows (maybe part of the sprites, idk how your system works) it would make it a lot easier to tell, plus it would make the world look 10x better and more polished. Without shadows, some things just are "there", and don't feel like they're actually interacting with the world.
Dialogue box changes: I get why the player starts off at NULL when selecting between dialogue options, but personally, I thought it felt weird and more like a bug rather than an intended feature, and it made it hard when I wanted to get through dialogue quickly. Also, I think the player should be able to hit a button like BACKSPACE, ESCAPE, B (on controllers), etc. to select the dialogue option that exits the dialogue if one is present.
And that's it! I think I may have had some more feedback that I forgot about, but those are the main ones I could remember! I would loooooooove to be a beta tester when the game is ready for beta testing, and I hope you take some of this feedback to heart! As a colorblind person, the bullet color changes would be much appreciated! (Or at the very least, a colorblind mode so players can decide for themselves!)