One great storytelling experience that I was sucked into (and have repeated 4 times now) is Final Fantasy IIV, and I have yet to play another game that has more depth or felling in it. There are so many things that make a good storytelling experience, but I think that one of the main things I look for is believability, because it is what makes the experience real and draws the player in.
Stories in games are usually told by a character, NPC’s or a narrator. But in the world of MMORPGs, of which I am not very familiar with, the worlds are dominated by human controlled characters, and it’s these that create some of the most interesting stories. For example, when people wage war on each other, and I’m talking about hundreds of people invading a city populated by other ‘real’ people.So I guess that a game can make a great story and not just be made by one.