I am absolutely fascinated by this game's mechanics and concept. It really shouldn't work to be totally honest (not being able to see the player seems preposterous), and yet it sort of does. I wasn't expecting it to go a sort of stealth/puzzle game route, but it honestly just comes together quite nicely.
The obvious feedback I can give is that the game would really benefit from actually having lighting, or at least some facsimile of it. It would make it easier to identify where the windows are (I found myself several times stepping out in front of one and then panicking while I tried to figure out why my little bar was going down). I also think it would be cool to be able to actually see a player shadow while in light, so there was a sort of trade-off where you could briefly see yourself, but your bar would be going down too. (Sorry, I really like this conceptually, so the brainstorming game dev part of my brain is kicking in.)
Overall, this is really cool. I could absolutely see the idea being expanded on.
Oh, and the little green dude rocks.