Halo 1 and 2 are my favorite shooters ever. AI and gameplay FAR beyond anything else at the time including Half-Life 2 which IMO is overrated. That's not even considering the multiplayer.
Wolfenstein: The New Order deserves a mention as well for putting single player shooters back on the map. Incredible game not afraid to push the envelope.
Thanks to another commentator I realized that Disco Elysium counts for this category and absolutely has to get my vote. Dark Souls is solidly second place.
There has never been a game yet that has the massive fucking balls of Disco Elysium. Imagine releasing a game about substance abuse, mental illness, and communism to critical AND mass market appeal.
Think about how many games don't bother to say ANYTHING at all. And then there's Disco.
Played thru halo 1 and 2 on legendary in the master chief collection a few months ago and it was just as fun if not more fun than the first time in the 2000s. Amazing games to this day fun all the way through.