Greatest RPG of all-time?

It's final fantasy VI.... end of story

Winner goes to Chrono Trigger.  Runner Up: Planescape Torment.  Honorable Mentions: Mario RPG,
 
This is not debatable. :)

Hmm... what defines an "RPG" nowadays? Tough to say. 
 
But I'll say Baldur's Gate is tops, Knights of the Old Republic is a damned close second.

OoT is an action / adventure RPG. it is the best.

Okage: The shadow king.

Uncharted 2. Best third person shooter, best action-adventure game, best tennis simulation game, best game to feature working handguns, best role playing game developed exclusively for the Korean MMO community.

Fallout 3.

Still Chrono Trigger.