hmm ... let's see. Realm remains my best memories period, and the lady sleeping in here I met there over a decade ago. She brought me to WoW in 2007 which I played heavily until Crapaclysm came out. When I heard the Kungfu Carebear expansion was coming, I took a significant break during which time I went to Aion, Neverwinter, Rift, and Wartune. Have Star Citizen...still not decided on that one yet.
I've played EQ 1 (back in its day), eq2, Horizons, UO, DAoC, Project Entropia, STrek Online, Kingdoms of Camelot.
Single player/non-mmo MPlyr: Starcraft, UT2004&7, Dungeon Keeper, Interstate 76/82, NFS Most Wanted, Grid 1, Bioshock series, Monkey Island series, most FF games -- of which 7 is god, Dragon Age series, most bioware games including Baulder's Gates and Mass Effect series, Might&Magic series (and Heroes of), Neverwinter Nights 1 and 2, ---Legend of The Dragoon, The Witcher series (badass), Assassin's Creed 1 (got tedious), Terraria (842 hrs worth and still going), Empyrion - Galactic Survival, Pax Imperia 2, Painkiller (best single player FPShooter I've played), Mafia 1, Just Cause 2, Mob Rule, etc...there's at least 3x as many. I also have NES, SNES, N64, Gamecube, WII, PSX, PS2, and C64 emulators...fully loaded with games.
Edit ... my god, I almost forgot Dark Cloud 1 and 2 lol