The lock delay feels a bit too quick, making it tough to perform precise, last-minute slides. It would be great to have some form of DAS, even if it's slow.
The clear mechanic to replenish the light is an interesting concept, but it feels somewhat pointless when you can just use the O piece in that one specific spot.
When you make a mistake, it's not easy to fully clear the area. Maybe the game could be more forgiving and create some kind of explosion that causes nearby blocks to fall and flatten out any holes. This could even lead to a chain reaction, clearing multiple lines in one go. Or it could simply be a traditional explosion that removes nearby blocks.
An idea I had was to have 3 magic cubes which you can use at any time to replace the current piece with this cube, and the use the cube to collide with existing placed blocks to clear them or the area, would be kind of like having 3 lives since the wouldn't replenish after each use. This might be a bit too complicated, though.
I'm suggesting this because after making a really bad mistake, I lost the motivation to keep going. It felt impossible to clean up, and the only way forward was to restart and lose all my progress. I tried to beat the game twice but made a terrible mistake both times.
It's a cool concept, but I think it's missing something to make it more engaging. Perhaps you could have short rooms with a piece blocking the exit hole that you need to clear to go lower. Or maybe add multiple paths, this could also make mistakes more forgiving.
I'm just throwing out some ideas. Even if they don't help directly, they might inspire other ones.
Well done, the design is very clean and has a lot of potential!