Without a doubt the best role-playing game session I have ever watched (without, unfortunately, attending the game myself - I was a mere spectator) was a game of Immortal - a role-playing game about immortals in a strange, futuristic world (see the link below for more information). There was nothing special about the game itself but, the gamemaster in that session: he was a God in the disguise of a GM - an unequivocal genius.
When the game started, the players (who hadn't met each other before, this was at an RPG convention in Finland) had a pencil and an empty A4 sheet of paper in front of them. Nothing more; no dice, no manuals, nothing. Just a plain pencil and a paper. Needless to say, the players were very confused.
Now, the GM dimmed the lights in the room, and started describing a scenery to the totally clueless audience he had. Everyone was paying 100% full attention to the gamemaster (quite a feat on its own, that), waiting for an explanation to the bizarre situation they were in. It never came. Instead, the GM described the scenery, the looks of each player character and then started leading them through a series of events. Then, at some point, he stopped and made some questions to each player and, depending on their answers said a single word to each player and told them - with a very detailed description as to how - to write that word on the piece of paper they each had.
This went on for several hours until a dim spark of comprehension started shining on the face of one of the players - that player had realized what was going on, and he was clearly awed by the genius of the idea. The players were on an introspective mission inside their own heads; a mission to figure out who and what they were, as role-players, instead of how good their characters were or how they could improve them. For the whole of the time, the GM had paid very close attention to what and how the players spoke to each other off-game, how they treated each other and how it affected the way they treated each other in-game, and made notes.
At that point I felt compelled and obliged to walk up to that one of the players who had understood. I tapped him on the shoulder and told, half to him, half to the GM: "as a reward to what he has achieved, this player's character suddenly feels a tap on his shoulder but, as he turns, he does not see anyone. Instead, he notices a delicate red rose in his hand and hears a silent whisper, much like a relieved sigh". Then I walked away as the target of half a dozen completely clueless, blank stares and two smiles that conveyed comprehension.
--- edit: Jan 08, 2002
I forgot to mention, the genius of the GM did not end there; I presented an element of surprise, both to the players and the GM. Yet, he accepted my intervention in the game and managed to turn that rose into an essential part of the final solution that concluded that role-playing game session.
--- End of edit
I can - without fear of losing - bet my place in heaven on that after that session there was one person, who had never before felt as rewarded about attending a role-playing game session. Not because of what I did, but because of what the GM helped him understand.
More information about Immortal, the role-playing game: