Hey NoeL, just beat the quest. I have a few remarks:

1 - The enemy sprites are great in general. I think the wallmasters need a bit of work though. Given the perspective, the side-views look like the palm is at a different angle than the up/down views. And I guess maybe the knuckle near the thumb is a bit too square in the clenched fist frame.
2 - At least in terms of how I've seen it used, the waterfalls always appear to be too wide. Although I guess this plays into how you were aiming to avoid the requirement of using layered transition tiles. With that in mind, I don't know if there's anything actionable about this remark.
3 - I really liked the backgrounds in the side-view passages and item rooms.
4 - I like the dungeon perspective a lot. I've made a few attempts at that perspective and I'll definitely use this as a reference in the future. I think the southern edge of the side doors might be too straight though? Is there enough room to possibly have the southern edge of the side doors angle down a bit? Does that look good?
5 - I would really like to see how you would do diagonal walls in your dungeon perspective.