lol its like if a game has good graphics is suddenly said that people only like it for the graphics.
Imagine this for MP:
16 players in massive city. Objective survive: you can explore the city for items which will be randomly spawned in different buildings,rooms,furniture etc. and when confronted with other players you could either team up or kill them for loot. Kinda like Day Z. Night comes and tickers come out. Last man standing after the ticker assault wins.
This is sort of what I'm thinking too. Maybe a few different scenarios to be tossed into. Another would be you're on a team from the beginning, against another 1-3 teams, and each starts on a different end of the city and the goal is to make it to the center to grab some item before the other and then get the hell out of the city with it.
So you'd have team-based puzzle-solving, traversal, platforming, etc, mixed in with setting traps, ambushes, and standard gunplay.
Though I am afraid that any open-world is too much to hope for. Doesn't look like the single-player has it, after all.