After playing this game for a few more hours now and having recently unlocked Mars..I have to say, I really think this game would have benefitted from being a traditional single player (with co-op) campaign. In a way, the open ended, 'social' experience almost feels a little shoehorned in. The only things you'd really be losing out on is:
Running into people randomly as you play, which mainly feels pointless anyway.
Public events, which I haven't even seen yet after 10-20 hours.
And the Tower, which outside of a random funny dance off, really doesn't need to be a social hub. I'd muvh prefer NPCs who I could actually talk to and learn more snippets about the world/lore from.
Back my point on how this should be a single player campaign. I'll start off by sayingthat the gameplay is solid, and the environments are beautiful to look at. Encounters are usually quite fun and there's a good variety of enemies. That's a really good base for the campaign. But cut out the crap from each planet with the repeated running through the same areas and excessive horde mode defense. Obviously the areas would be designed with a more focused experience so slightly less open, but with more to do. Have one or two traditional missions per planet, and skip the pain in the ass endless to and fro with orbit and painful load screens. Have a couple cutscenes to help pad out the story and add more context to things rather than just the odd line from ghost.
It's late and I'm about to go to bed so I probably haven't done a good job of getting my thoughts down on paper but ahh well.