This is a thought exercise I saw in Rock, Paper, Shotgun a while ago. It is one of those posts I've been meaning to write for a long time but... uh...I kept getting distracted and didn't do it.
Anyway! Here is the hypothetical situation: Imagine that one day there is some weird cosmic event that wipes all games from existence. Not only that, anything related to those games is also wiped: game boxes, manuals, magazine articles, sites, etc. Even people's memories of those games existance are gone. Except you are given the choice of saving one game from this gamepocalypse.
Now think carefully about which game you want to choose. First because it will probably be the only game we'll have to play for a while. Secondly since it will be the "first video-game in the history of humans" it will influence a lot of developers in the short term as they try to figure out this new medium and on the players as they come to expect games to have features like that one.
I gave a lot of thought about which game I would choose but right now the only one I can think of is Morrowind.
Yes, I know there are lot of other games who do story or gameplay better. But I have quite a few reasons why I'd choose to save it from annihilation.