RuneScape, always good to get back to some nostalgia (OSRS)
MapleStory, servers are laggy and unless you play on Reboot server (compared to Runescape ironman mode) it is heavily pay2win. The community is absolutely cancer.
Blade & Soul, I really enjoyed BnS but only with friends - alone is damn boring.
C9: Continent of The Ninth Seal, same for BnS, great game but sucks to play alone.
Guild Wars 2, Amazing game, not sure about the rest - haven't played it for a long long time.
Neverwinter, heard a lot about it however I've never played it myself.
TERA, same as Neverwinter - positive stories, never tried it myself.