This game is what I wish every stealth game was like. It's got about 1 mechanic and several sub-mechanics that build upon it, and that is that:

There are enemies. They will learn from whatever you do every time the light is on. In the dark, they will not learn.

But each and every individual action and animation save for travelling on elevators is able to be copied by the Echoes. If you shoot in the light, they learn to shoot next time the light comes on. If you run, so do they. But! If you wait until the lights go off to run and shoot, the Echoes won't be able to do these things, and it can provide you with a detailed advantage that you can customize at any time.

So, cool idea, but how does it fare in game? Pretty dang well, I think. The diagetic HUD shows you exactly where the enemy that saw or is trailing you is and how far you can sneak around before they notice you. The AI isn't super unforgiving, and not super easy to avoid. I think this game is designed great, with ample reason to explore and engage with its systems. The story is enjoyable, too. I loved the dynamic between En and whoever is on the other side of the call.

9/10. I didn't experience any bugs or anything and I got this using a key. My only criticism is that it gets pretty repetitive after like 4 or 5 hours.

A hidden gem. Perhaps its stealth can sometimes be repetitive, but the atmosphere of the game, the sensations it transmits, the world it creates, and even its story (more cryptic than it seems, but interesting) make this game very worthwhile. I once read that someone said that this game reminded them of the short film "Magnetic Rose" by Satoshi Kon. I completely agree.

(sorry for my english)