DAoC
Was probably my first real mmo, played that starting in beta and came back to it like 3 or 4 times over a span of many years.
Fun stuff really, let alone those giants they send to "destroy" the towns at the end of beta, or those arachnid nests close to starting villages, "train" was a lethal word those days.

Was really awesome to see 200+ players in one spot, ready to fight each other.
NeoCron
Incredibly awesome game, probably the best if I had to chose one of those I ever played, too bad they had no luck with publishers and game went steadily downhill.
Was like EVE only as a shooter, no perma death but still killing and looting anyone anywhere anytime, that is a good foundation for a fun game.
And the community was very good, too. Probably because the usual kids did not last long there. ^^
WoW
From Beta to shortly after WotLK release, it was good when it was new, drifted into an endless daily grind and PvE fights that were more of a dancing coreography than actual fighting.
I loved tanking, I tanked with my pally in vanilla back before people believed pallys could tank. Had the full deathbone guardian set and was a better tank in scholomance and stratholme than most "normal" tanks I'd say.
Had a hunter that was super tanky with 3500 HP running lvl 49 BGs.
Had a super tanky warlock, that ate everything but the best rogues for breakfast.
Had a druid, my most successful one, tank ofc, went to see and beat illidan, had 20500 HP unbuffed in TBC times (lvl 70), survived a 27000 hit from brutallus np^^. Absolutely unkillable in PvP by means of physical dmg, hunters would be way oom and rogues crying in the corner before even getting through half of the HP.
I heard a lot of wow through friends and how it changed lately, how they now cater to crybabies and complete noobs,
strangely, even before that, I never felt even a little urge to look at wow again after I quit.
SW:ToR
A fun game really, fun to play through the story once, but gets boring from there on, sadly.
EVE
I pretty much did everything there you could, except FW.
Flew lvl 5 missions in bulk back when they were able to spawn in highsec, started that with a NCR + domi, ended up with a nightmare + rattle, was so proud of my setup.

Lived 6 months in a C5 WH with static C5, made billions every day with my friends there, killed and robbed a few random people, so much fun.
Went to null and became a renter of red alliance, later a pet, went up and proved our worth in combat, lived in insmother first then in geminate, was a great time really until geminate fell and everyone scattered across the stars...
Always traded a lot, sitting in Jita first, then supplying several null regions with certain stuff.
Had 3 t2 BPOs, 5 carriers, 2 dreads, 1 JF, 2 normal freighters, orca, rorqual, 2 nightmares, 2 golems, a vindicator worth 10b with mods with 2500+ dps and sufficient tank, tons of t2 and some t3 and pvp ships for everything from small roamings to fleet fights...
... cash and assets were some 200b in total when I stopped playing, not even counting the 7 well skilled chars that I had.
Played some 4 years in total, was a great time, too bad EVE is so time consuming.
FireFall
Played back in beta, this one is pretty old already, a shooter mmo, revamped everything a hundred times, now with a chinese kraken in command, promoting p2win.
I am really sad to see how this one went downhill, this could have been a really, really good one.
Warframe
Not an mmo really but well, multiplayer, played only cause of my friends, only mentioned here because of it's uniquenss, has the most horrible community of stupid arrogant little kids I have ever seen, and the biggest mess of (partly intentional) gamebreaking bugs and some designs that just leave you breathless for how anyone could be so dumb to implement it in such a way. Yet, this one is quite succesful, a very stupid game attracting mostly very stupid people it seems.
Honorable mentions:
Tabula Rasa, looked great at first, didnt keep what it promised
Perpetuum, like EVE with robots, probably had potential but so do many.
Vanguard, wasnt really too special at all.
AO, had some interesting moments, but didnt play long.
SWG, played a little bit way back when it was new, didn't really convince me though.
DCUO, played long time ago, looked fun, awesome intro^^, p2win ruins it though, also looked a bit half baked.