> I wouldn't call WoW the first that defined it, or even the first wildly successful one that did
> Then again, maybe there's something very different than WoW and EverQuest that I'm not aware of?
Agreed that WoW did not define what an MMO was, a lot of the perception has to do with timing. More people had access to a decent computer and reliable internet when WoW came out than in the mid-late 90's. I think of BBS door games and MUDs I played as a teenager as what defined MMOs (personally, not generally). To me those were huge, playing games with random people I would never meet at a time when the other options were 1.) passing a controller around or 2.) literally carrying computer equipment to random LAN parties.
But it was UO that made the big commercial splash, the marketing was on point. It was this new thing called a Massively Multiplayer Online RPG. This new world where you could be someone else. A place you could just log in to go fishing, or save up to buy a boat to find better places to fish, hunt and mine ore. And placing your first home, which was probably the smallest most useless building in the game, was yours. Your little safe haven in this new crazy virtual wild west that didn't stop evolving just because you had to go do homework. I was obsessed with MMO's after that, and obsessed with being one of the first to play. Luckily I ended up in one of the first areas to offer cable internet in the late 90's as these MMO's were doing beta test sign ups - having cable internet usually got you in early.
EverQuest was the game changer (for the more mainstream gamers, Meridian 59 was the first 3D MMO and it came out before UO). I remember the first day in EQ, standing outside in the noob area and the chat was full of people in complete awe. There was nothing even close. I ran around with a couple other people trying to see as many locations we could get to without dying and not even trying to level.
Shortly after EQ, was AC - Asheron's Call, which gave us the beautiful 3D world without the annoying (loading)zones of EQ and others, freedom atleast. I probably played AC the most while mixing in others I had missed or got beta invites. When WoW came out I refused to play it (still haven't), I was a big fan of Warcraft. I thought what they did to it was sacrilege and viewed it as the place for the new gamer-generation to pick up their participation trophy cause they couldn't handle the grind of a real MMO. They should suffer as I suffered.
As for MMO's that I found different, EVE for sure.
Project Entropia - was/is? the only one I know of that used real money for the in-game economy. You could literally play for free and make money from selling stuff from hunting, crafting, mining. I had about $200 I never cashed out (earned, not deposited) and I think my account got purged from not logging in for 2+ years at one point, or so an old email said would happen.
World War II Online - this game was def for people who would do cosplay US Civil war reenactments, but for WWII. Was a little much for me, but it was the foundation of my love of Battlefield games.
A Tale in the Desert - this one was fun when I played, I loved the concept. Its played in 1+ year long episodes where society has to pass test and challenges and work together or not. If you like crafting with a large side of real social politics that will determine if this years episode is "won", this is the game for you.
Hattrick Football Manager - browser MMO that is unlike any browser game I have played since (I played in the early aughts), if you like manager type games it was addicting. So much so I am right now trying to not make a new team and get sucked down that rabbit-hole again: https://www.hattrick.org/en-us/
Mortal Online - this was the last one I was actively engaged with, as I was trying to re-live the first days of UO, I went back to UO many times and nothing else ever felt the same. MO was trying to re-live it as well. No levels, huge crafting, hunting, exploring taking over cities. You could collect other people heads as trophies. It was ambitious and promising during beta - then completely unplayable after launch. MO2 came out recently, not sure how it is.