...continuing Joel and Ellie's story that is.
It's not just Naughty Dog's writing that made The Last of Us so amazing, but also the the brilliant performance of Troy Baker and Ashley Johnson as Joel and Ellie.
A lot of people think continuing Joel and Ellie's story will make the first one seem less meaningful - first of all that's ridiculous because if you don't like The Last of Us 2 the first game still exists and a second one won't change that. Secondly even if the writing is a little forced, Troy Baker and Ashley Johnson's performance will be just as amazing as the first one, maybe even better because they have both been in other games since The Last Of Us (Troy Baker even made me tear up a little in Call Of Duty). Naughty Dog did a good job with Nathan Drake, so they would do just as good a job with Ellie. In fact I always thought of Ellie as like a young female version of Nathan Drake. If they continue Joel and Ellie's story we would likely see the return of old characters like Bill, Tommy, Tommy's wife, and well the rest of the characters are dead so that's probably it, but other characters like Tess and Marlene could show up in flashbacks that would show us the 20 years after Joel's daughter dies, and things like how Joel met Tess, and the rise of the fire flies, and Joel joining, and leaving the hunters.
(Am I the only one that wonders why the online is fire flies vs hunters, aren't they kind of on the same side, it should be fire flies vs military shouldn't it, but what ever.) We would likely see new side characters as well, but the sequel, if one even exists, as much as I would love a Last Of Us trilogy, the first one would make a good stand alone game, but the sequel should continue the story of the first one, yeah showing more of the world would be great but it should also continue the story that it established the game to be about. Show us more of this world, but do it through the eyes of one central character, or characters depending on if you'd prefer it to be Joel and Ellie, or just Ellie, or just Joel but personally I like Ellie better.