Glitchspace is a Portal-esque deconstruction of video game mechanics that's not only beautiful, but more accidentally also pretty good at teaching math.
In the game you're alone with the protagonist and her thoughts while she walks through New York. In reality you are alone with yourself and your thoughts while you move pixels over your screen.
I'll be unfair to three games with the following comparison: In The Kingdom is like the gameplay of Doom paired with the creepy, surreal atmosphere of Silent Hill. Or something something.
It's impressive with how much humour the game tells its honest story of half-truths. Any other adjectives to describe it would be much darker. (Trigger warning for domestic violence and homophobia.)