mutliplayer in prototype
and a "Toy Box" (like Crackdown 2's not Crackdown 1's) mode to allow people to make good machinima with the game
i think the co-op could be well done if it was a separate game mode (like co-op for Modern Warfare 2 and Splinter Cell Conviction's are)
and multiplayer could be like "everyone versus Mercer"/"cat and mouse" game where people play as the military or the super-soldiers trying to take down one player who is Alex Mercer or some other "custom" mulitplayer avatar (it could be like "Pitch Black" mode in "Assault on Dark Athena")
what do you guys think?