Man UO is such a unique game. No other game let's you be a dungeon spelunker who's sole job is going into dark places and lock picking chests for gold and stabbing the occasional lizardman.
when i was a kid and before i had my own PC i used to dream about playing this game.
i was excited about just sandbox and the mundane shit you could do. seemed like a real fantasy-themed life simulator in an age before MMORPGs were codified in any ways so things were crazy experimental.
only ever got to dabble with it briefly much later. only other thing close i've found is Project Zomboid.