In response to the Discord post, I though I'd start this post with my thoughts, and welcome everyone to reply with their own.
Let me start by saying I play a lot of co-op games. From The Division to Destiny to Elite Dangerous to No Man's Sky (YouTube.com/TheGamersShow1) to VR games like Karnage Chronicles, Battlewake, and Star Trek Bridge Crew (YouTube.com/LiveFromTheOasis.)
Playing through a story mode together can be a whole lot of fun, and when the story is good (and the game supports multiple characters per user) replaying through a good story is also a blast. I've lost count of how many times I've played through the Halo games with family and friends, and we've also played through Destiny 1 and 2 multiple times. So my first point would be allowing users to play through the story multiple times using different characters. And I'll add that allowing a user to have multiple characters of different classes is huge. With Destiny having three different classes, each time we replayed it was fun to be able to level up each one of the classes.
And when you're looking for something different to do, it's nice to have weekly challenges to work with your friends on. When we're not on the frontiers killing Thargoids in Elite Dangerous, we'll often take a break to work on Community Goals. Same goes for Co-op missions in NMS. Something that is very cool in Skyrim and ESO is the ability to buy and decorate your own home. Taken a step further, base building like in No Mans Sky gives players endless fun as they get to build their dream base.
So for now, I'll leave it at this:
1 - Being able to play through any story mode with friends multiple times, with the option to play with a different character each time. Bonus points for being able to have multiple characters of different classes. 2 - Weekly challenges or co-op missions to give friends something to do outside of the story.
3 - Being able to make and save up enough "money" to buy your own home and decorate it. Since the game is based on 4 players, you might have four homes available to be purchased in each town / city / district. This reminds me of one of the Fable games where you could buy one of the many homes and then decorate it - very cool. Bonus points for custom home building once you can afford to buy land ;-) Peace out, Grey