Darkness in general was pretty much the constant obstacle in the game for me, and I found myself reloading saves more often than most other jam games to help find my bearings (sometimes even rushing down corridors before the screen could fade to black to get a quick idea of the layout). Even with map drawing I'd often get completely messed up by fighting an encounter mid-turn and losing track of my direction (since the compass isn't visible either in darkness).
While I like the Skill-based solution-approach to combat, it made darkness combat a non-option when fighting anything that required more strategy than bats, since I'd often get mobbed while floundering to select the correct character and their skillset/escape without the UI. My heart sank after wiping out at the cockatrice encounter; not because I'd have to grind, but because I'd have to go through that damn dark corridor twice to get back to the save room and back.
I persevered though, and aside from the UI hiding, I never felt the game was particularly unfair or didn't give me the tools to succeed. I liked how you couldn't tell apart slime colors easily in the dark, and honestly felt that better monster hiding alone would make for an interesting challenge given the limited skill slots, rather than hiding the entire battle menu for several turns as well.