I looked for a bit and didn't see this answered, many apologies if it has been addressed before. Here goes.
One of the things I noticed that I had forgotten about after returning to the city lately was the CoX both made it very easy and very difficult to do missions with teams. Let me explain that sentence. It was very easy to team and do missions, more so than basically any mmo previously and to this day still stands out for making it so easy to play with your friends. Because of the way the mission and contacts and story arc system was created, though, it didn't let you really share progress with your team mates. You could all do the same mission, but it was the leader's version of that mission and only gave that leader story progress. This made it easy for players to play together but made it harder for stories to have any kind of impact since players would skip around getting pieces of stories here and there. This makes it harder for players to have memorable moments from content since they have a harder time following a coherent narrative, identifying with characters, etc. Everything becomes a beat-em-up of faceless mooks.
This isn't to say CoX had bad writing or the content was lacking. I recently stuck my toe into praetorian and the content and writing there really stands out, especially compared to stuff from earlier in the game's development. It still suffers from the same issues when grouping though as players will get it rushed (groups tend not to be happy about one person stopping to read dialogue) and in pieces. This doesn't even take into account the moral choices and story paths that the leader can choose in praetorian stories that the others in the group have no say in.
I know CoT devs have chimed in with ideas on how story choices will be handled in groups before, but I don't remember hearing anything about how stories themselves will be handled. Some games like WoW would allow players to share quests and complete them together, but they would need to have certain requirements done in order to do that, be it certain faction reputation or having done other quests or gathered items first. Basically it just let them skip talking to the quest NPC. CoX let everyone play but only in the leader's version of the quest, it wouldn't introduce the relevant contacts to the rest of the group or move their reputation or anything like that. It still usually gave everyone any special rewards like temporary powers related to completing the quest though, so you only really lost out on the story itself.
I think the way CoX handled story arcs and grouping was good, but could use a little work in order to make the characters and story come to life. CoX actually had amazing writing and a great setting but a lot of players I've spoken with couldn't say much about the setting and characters as they never really experienced it firsthand through the game due to this. Sure, there is a ton of amazing fluff in the wiki and elsewhere but when you just team up with your buddy and punch 500 mooks in a warehouse none of that writing and flavor gets to that player.
Later content helped with that a bit by putting in little cutscenes and some dialogue. Perhaps the best answer is simply more cutscenes, staged encounters, puzzles, dialogue, and other ways players can directly experience the story? Perhaps a focus on making individual missions be relatively self contained episodes that, while being part of a larger narrative, make sense and have an interesting arc by themselves? This could especially help players that are not able to commit large chunks of time to a game in one go.
Perhaps another way to help would simply be moving more of the story into the missions themselves rather than talking to a quest NPC. That is related to the point above. Because the story is shown during the mission, everyone on the mission sees it firsthand even if they never spoke to any contact outside.
I got the impression CoT was aiming for more handcrafted story content with branching story paths, but all that work wouldn't mean much if people only see episode 1, 7, and 56 of the story because they jump around with friends and outlevel it. Especially if those episodes are just "beat up 10 guys in this warehouse".
I'm curious as to everyone's thoughts on this. I love having it be easy to group with friends and would hate to sacrifice that for ease of grouping, but in this day and age it would be nice not to sacrifice having a memorable player experience to do so, which CoX does to some extent.