Wow, this is quite difficult (omg, Battle of Olympus had a GB version ?!)- esp. with the DD clause- and they have to be good/best too...
PC
Albion - PC-RPG, that still isn't on gog but supposedly is really gud ;_;
(Planet's Edge 'though it's also on FM Town the japanese PC, dunno if that dis-counts... ?)
NES:
Kickle Cubicle - the best iceblock pushing puzzlegame
Kabuki Quantum Fighter - the best hairy weapon game (I know of) I could never beat
snes:
Brainlord - if Lufia were an Single-Party with Faery Action-RPG
Young Merlin - Walk 'n Click game with absolutely no text and adorable little enemycritters
King Arthurs World - best Ride of the Valkyrie... I mean... the game is fun
Mega Drive:
Warriors of the Eternal Sun - clumsy, difficult (insanly around the end) but interesting RPG that never got it's announced sequel
and since there cannot be a best RPG it deserves a mention
*staring at own gamelist* obscure japanese games
saturn: Wachenröder (nice Tactics-Variant with overheating weapons)
no idea about the quality, since I haven't played them very much:
Neo Metal Fantasy (PCE), Dragon Knight Glorious, Oni Zero, Mystic Dragoon (PS1), Terra Phantastica (Saturn)
Virtual Console (JP)