Quick review - Ehhhhh.... Alright... I guess?
Long review - A really interesting game, with plenty of interesting concepts. It starts out really fun, and a bit mindblowing. When you find a new tool, and discover its new abilities, the game becomes a little more interesting and fun - but that new fun doesn't last long, and it becomes a bit of a grind. Some of the puzzles are fun to figure out, some are kinda arbitrary and frustrating. I rage-quit really hard three or four times, and looked for hints or walkthroughs. The atmosphere feels a bit like Portal, but is much more cold and boring.
Perhaps the biggest problem I had with Antichamber is that I rarely felt like I was accomplishing anything. There was very little incentive to keep me playing, other than to just finish it. And I was extremely disappointed upon finishing it.
The game felt really uneven to me. It starts out awesome, then gets boring, gets fun again when you find a new tool, gets boring again, repeat.
Still, it was a really interesting experience, and I am glad that I played it. Would I play it again? I lean towards yes. Perhaps I'll give it another go next year, when I don't remember everything, but remember just enough to not be frustrated.
The price ($20) is a bit high, in my opinion. This felt closer to a proof of concept than a full game, and should be given a price to reflect that. I was able to buy it for about $7, which I am happy with.
According to Steam, my playtime was about 10 hours.