Skyrim'll easily be supplanted by whatever newer shinier ES comes next. Morrowind's cult status came upon it for having a more unique and individualized setting, as well as a ton more characterization, which has only cut down across Oblivion and Skyrim.
Souls don't really offer much new to the action RPG genre. The main distinction between Dark Souls and Zelda is difficulty and tone. The difficulty is largely by removing features (like pausing, saving, jumping, etc) which is stepping backwards more then forwards, and the dark tone bubble is going to burst eventually (if it hasn't already). Also, while literally everything else in the game was horrible, Dragons Dogma basically killed the other three in "How to fight big monsters properly" (with a leg up by borrowing Shadow of the Colossus).
Portal has decent odds, but probably in a more niche fashion in the same subgroups that still replay Myst.
LittleBigPlanet is basically the main competition to Mario these days and probably gets the nod for introducing the console level editor to widespread use.
