I am actually worried that the next game is going to suffer from sequel syndrome when the previous game is so good it will be almost impossible to actually make the sequel as good as Arkham City.
I am not worried about the villains. Many of the ones you saw here you never met or had tiny encounters with them only. By the way, even besides those on whom the file is shown there are many other villains. Some of them were even displayed in Arkham Asylum. One I can think of is pair, Tweedledee and Twiddledum. They are ridiculous, but if Rocksteady can make Robyn and MadHatter look bad ass they can with these too.
Then there is man-bat, firefly, Maxie Zeus (we saw Zeus casino), killer moth, red hood, Joe Chill, Anarky. Plus various ones that appear JLA , bit I'd rather JLA have nothing to do with this.
What I am worried about is what location it could possibly be. I realize there is Gotham City, but it creates problems because it has to be very large. Xbox 360 May have a limit on how much of the city it can hold in memory and keep loading as you move, so I hope they do not divide it into chunks as has been the custom with games like GTA or recent Prototype 2. If they make it seamless they'd have to re-use a lot of buildings and it will appear "cheap"