I have been gaming since 1982. I started with Star Frontiers (TSR), Boot Hill (TSR) and Wild West (FGU), then Spacemaster (ICE), Chivalry & Sorcery (FGU), Bushido (FGU), Twilight 2000, and James Bond (VG).
I started GMing with Wild West, Runequest and Stormbringer, but it wasn't until I found a pile of cardboard sheets with attack tables, critical charts, and tons of spells that I found one of the two best games ever, Rolemaster.
It wasn't until 1992 that I finally played D&D, and perhaps that is the problem. It's like I was brought up on anime and manga and then someone forced me to watch old OLD (pre WWII) Looney Tunes and said, "isn't this the greatest?"
Well, in a word, no.
It's my fault, really, I was spoiled.
After more than two decades of gaming, my favorites are Runequest (3rd), Rolemaster (2nd+3rd), Spacemaster, DC Heroes, Champions, Ars Magica, Mage, and, with the right people, Werewolf.
I have also played Villians & Vigilantes, Marvel Stupor Heroes, Aftermath, Space Opera was pretty cool, but that's all I remember of it, Wooden Ships & Iron Men were theirs too. I made a character for Flashing Blades but never played it. I also played Twilight 2000, Recon, Paranoia, Shadowrun, Earthdawn, Jorune, Cyberpunk, GURPS, Mercenaries Spies & Private Eyes, Tunnels & Trolls, Traveller, Torg, Pendragon, and a few others.
GM:
Champions
DC Heroes
Mage
Pendragon
Rolemaster
RuneQuest
Spacemaster
Star Frontiers
Stormbringer
Werewolf
Wild West
Player:
Aftermath
Ars Magica
Boot Hill
Bushido
Call of Cthulhu
Champions
Chivalry & Sorcery
Cyberpunk 2020
DC Heroes
D&D 3.5
Earthdawn
Flashing Blades
GURPS
James Bond 007
Jorune
Mage
Marvel Stupor Heroes
Mercenaries Spies & Private Eyes
Paranoia
Pendragon
Recon
Rolemaster
RuneQuest
Shadowrun
Space Opera
Spacemaster
Star Frontiers
Stormbringer
Torg
Traveller
Tunnels & Trolls
Twilight 2000
Vampire
Villians & Vigilantes
Werewolf
Wild West
Wooden Ships & Iron Men