I hope it's a smaller version of DayZ. Survival co-op where you gotta eat, lots of melee, protecting turf from crazy bandits, minimal shooting, co-op teamwork to fortify areas, day/night cycle, moving to different zones after a few "days" in one area, etc. etc.
Heh, that would be awesome, but it's probably way more ambitious than what we'll see. I expect a horde/arena type co-op mode, and maybe some competitive deathmatch and objective modes as well. Basically the same as Uncharted, but more tailored to Last of Us's focus on brutality and conservation.