Several of my favorite gaming experiences are one-time, non-repeatable. Solving the Return of the Obra Dinn is up there, but it couldn't possibly be my favorite game because I can never experience it again.
Playing Dark Souls for the first time is the same thing. Discovering the world, finding the intricacies of the interconnected map, struggling with and overcoming challenging areas and bosses. The relief of unlocking shortcuts and the amazement at the maps connectivity. It was the first game of it's type I played, and it was phenomenal, but coming back to it never matches that first playthrough. And let's be honest, the bosses feel downright mundane after having played the later releases.
Disco Elysium affected me in a way no other game has. Its themes are so relevant to me that it struck me on a very personal level and it was an incredibly cathartic experience that will stay with me forever the way any great book would. I actually found it more enjoyable the second playthrough too, however, is it really even a game?