Anything from a simple quest for a lifeboat, to a mad rush to grab objects from all over the ship. And there's a fair amount of real-life tension to work with. Mind you, you only have to meet them so that they can do you a favor. And then the denoument, after you escape on a lifeboat. You have fulfilled none, some, or all of your tasks.
History is changed.
If you missed anything, things are bad, one way or another. I spent at least two hours playing through the endgame again and again, deliberately screwing up in as many ways as possible. Because you get a little summary of history each time. I was fascinated. Scribbling little notes about each one.