[satyrnein]

The game was called Passage; I still remember it very clearly. If you chose to form a couple, you wouldn't be able to squeeze into certain spaces to get certain treasure chests. The "message" of that mechanic, that being part of a couple means you have to forego some opportunities in life, isn't particularly controversial or novel, but "feeling" it through the mechanic was really impactful. (And that was just one aspect of that tiny little game!)

Similarly, there was a game called Brothers that delivered its punchline through its mechanics in a powerful way. (I don't want to spoil it for anyone!) I'm not sure if it's art or whatever, but it's something interesting and distinct from what you get in other forms of media.

Meanwhile, I enjoyed both Gris and Celeste, but purely on a mechanical and/or aesthetic level, and not really a connection to any deeper message.