It's really something special.
Conway's Game of Life is a well-known cellular automaton in which, every tick, the state of each of the cells on a giant grid is determined only by the states of its immediate neighbours in the previous tick. Despite its extremely simple definition, it is famously Turing-complete, which is roughly to say that it can compute any computable function.
And so, of course, someone has written a Life emulator, in Life.
Perhaps it's Life all the way down...
Robert Yang (who I've mentioned here before) made such a good let's play of the first room and corridor of Half-Life.
A "let's play" is traditionally a narrated video of one or more people playing through a video game. Usually they are just to document the video game so that it can be experienced or understood without playing it, but some of the best ones are made by people who know the game inside out and are able to add some amount of context or commentary to the play-through, drawing the viewer's attention to specific details and not getting side-tracked by any difficulty in progression. There are many great let's plays on the Let's Play Archive.
Robert Yang's video is not really about the game as it is played, but about the design of the game from the perspective of a level designer. It was made for a let's play event.
I don't think he has plans to do more but I would listen to that guy talk about level design any time. A couple of the comments under his post of the video are worth reading too.
Oh this? Just a film of landing on Mars.
PS. If you haven't seen NASA's "Seven Minutes of Terror" video, it's worth checking out. Those folks are crazy.
I watched this interesting talk on game design by Jonathan "Braid" Blow and Marc "Miegakure" ten Bosch. They espouse and explore a particular design aesthetic where the designer essentially plays the role of a mathematician. "Good design" then becomes a selection of orthogonal mechanisms (axioms), and an exhaustive-yet-minimal mapping-out of what's derivable (theorems), and then demarcation of the boundary. Since it needs to be fun, the real art has to come from crafting surprise and tweaking axioms to capture exactly what you want. They both make some very interesting points, and I thought this comparison with mathematics was a particularly cool and apt way to frame the ideas.
Watch it here: