What I want is they improve combat enabling you could counter more efficiently and more greater AI. The story could be a prequel,the game has many good story for a prequel or they could tell the story of Ellie and Joel again where Ellie know Joel's lie and kill him or forgive him. Or a whole new story.
Definitely the basement in Pittsburg. My first playthrough is on hard and when all the infected start coming,I use my hearing and though they were only clickers so I wanna kill all of them then I see the Bloater and start screaming: "That not a clicker,that not a FUCKING clicker!" I run the hell out of there. Definitely the most scariest part of the game.