As I've aged, my interest in competitive multiplayer games has waned. I find that I have no interest in fighting other players online, that I don't really care about the score I get, and that having those things present in a game tends to pair me up with players I'd rather not play with…
There’s heaps of mods for classic games to turn them into co-op, including Doom (3), half life, quake, aliens vs predator, etc.