Thanks for playing and taking the time to give such extensive feedback.

If it's feasible and fits the style you're going for, consider making the enemy pathfinding a bit more intelligent (from what I can tell they just head straight for the player ignoring any obstacles). There were a lot of places where I ended up just cheesing the enemies through a wall which didn't feel like the intended strategy. There was one room towards the end where you mitigated this by adding the little wall-shooter guys on the opposite end of the room to make this strategy more difficult than just engaging normally, so that's another way of dealing with it!

By this point I've finished all 4 of the main dungeons and balanced them around the bad enemy navigation, so I don't think that's going to be viable unless I'm willing to add a lot of dev time. Not sure if that's something I'm prepared to do, since this is already a very ambitious project for my means and skills, though it's something I'll definitely look into going forward.

Adding color-coded doors to the map. Seeing an unexplored path is certainly a clue that there's a locked door there, but it doesn't necessarily tell you whether the path is blocked by a standard key door, a boss key door, or a non-keyed door.

I agree this would be a nice quality of life feature. Definitely something to look into for the final polishing phase.

Making the fire for puzzles non damaging, or arranging them/giving them smaller hitboxes such that it's less easy to bump into them. I think I died at least once from clumsily handling the puzzles (probably on the one where there's a complete square fire fence around the four arrow blocks)...maybe that's just on me needed to working on my jumping skills, but it did feel frustrating to die on a puzzle like that. Again, this might also be something intrinsic to the style that I'm not used to. I know the fire in Binding of Isaac damages you when you walk over it, but you're also never required to do that so

A lot of people complained about the jumping/platforming in the early builds, haha. It turns out that there was a problem with the collision detection for pits/floor hazards that I didn't discover until fairly recently. I'm hoping this makes those sections forgiving enough that retooling a lot of the puzzle elements won't be necessary, but I guess future playtesting will determine whether that is the case.

Along the same lines, it'd be nice if there were a way to manipulate individual arrow blocks besides swinging your sword, or if their hitboxes were smaller to make accidentally triggers less likely. I never quite got the hang of how far I needed to be to only hit one block, so probably half the time manipulating the blocks was spent going, "[slash] Aw man, I accidentally hit two blocks... [slash x7]. Okay, this time I'll get it for sure! [slash] ...dammit."

You're not the only tester to have this problem, so that's definitely a valid concern. That's another thing to iron out when it comes time to polish. Not sure exactly how I'll handle it yet.