Last I checked, if you had an account from back in the day, you could still play on the servers, even with other people (there is still an active community on discord for events and raids and pvp and such).
But no. Don't play that abomination on steam.
Mine would be Anarchy Online. Still around, though FC has ran it to the ground and not too obscure, considering it used to be quite big before 2005ish, but almost nobody talks about it in EU and the few times they do is to comment on the dreadful launch.
But I doubt there's a game I've sunk more hours into, playing constantly from release up to 2011 and then on and off until last year. Eventually I figured out it's just nostalgia and it's not worth it anymore, the time, let alone the sub.