I don't like to like what everybody likes but if you don't like this you might as well give up on the whole industry.
It has perfect pacing, a progressive difficulty that goes hand to hand with the learning curve and a great atmosphere that intensifies gradually.
It tells you a story by telling you just enough for you to grasp it but also imagine how more deep and horrible the story truly is, in a good sense, and it has a satisfying ending.
And having in mind this is a puzzle game, you know, the ones that are supposed to be boring, this is a mind-blowing achievement.
And of course there's the portal mechanic, which is awesome and tickles your brain. This is a game that makes you think, which is a very unique thing to be honest, living in the dumb world we live.
I can only think of one bad thing about this game, being to short.
But since I got it for free and i've played it like 6 times the argument gets totally obliterated and i'm forced to give it a 10.
Get this game. Now.