Woah... this gave me some of the same vibes that Nameless gave me. Chills, but also an undertoned and (somewhat) relaxing randomized dungeon crawler, of sorts. I actually strongly appreciated the lack of music in the midst of these rooms, with little but the sounds of primordial machines meandering about at the edge of nothingness. Just as Mumei was, trying to remember things. The deeply personal touch to that dialogue of hers with herself through the notes left me in quiet contemplation, as did the epilogue once you acquired the pieces.
I actually really enjoyed the top-down perspective, though the tilesets for traversable wall segments did make it confusing. Tab might've been a better shortcut (or configurable) to get to the memory bank, but I thought it was a great solution to the core mechanic there. The light mechanic didn't really threaten me, as I was able to complete all three corners in one go without taking too much damage (just the occasional tower shooting at me). Balancing what to memorize with switching rooms strategically was actually a ton of fun, though I found I didn't need to remember rooms at all -- just swapped between rooms until I got a pathway I needed forward, or an item that let me keep moving.
This could develop into an awesome journey from start to end, of Mumei remembering things, events -- friends -- and I'd probably end up shedding tears by the end.