I’m going to choose one that is kind of both as it’s a favourite of mine and also a game I think everyone should play because it changed the game scene completely.
The game is Goldeneye 007 for the N64. It was one of the first games that I ever played so maybe I’m biased but it was a fantastic game.
The single player is fun (apart from the Jungle level) but the real fun was in the multiplayer. Four player split screen just never got old.
If they could ever get through all the licensing kerfuffle (Rare is now owned by Microsoft but Nintendo published the game but Activison has the Bond game rights) and bring it to the modern games with multiplayer over Live? I would buy that in a heartbeat.