I love the atmosphere. It's very pretty despite the shader glitches, which I think affect the gameplay more than the aesthetics (the only thing I noticed with them was the portals sometimes showing the wrong room). I messed up a few times because the doors didn't go where I thought they would.
I had my volume set low (apparently) so I almost missed there was music. It's a good thing some other commenters pointed it out :P It is very nice music.
The timer could be a little more prominent, with something to draw attention when it runs out. On my first attempt, I didn't even notice it, and was confused when I suddenly couldn't move anymore. I thought I had glitched and got stuck, but then I noticed the negative timer.
I don't seem to be fast enough to beat it, so I can't comment on what happens when you win :P