I've said it before in regards to other games... I would love a co-op option in my singleplayer games.
However!
If it's multiplayer/ co-op as we've mostly seen it, the resistance and objections of other people here are fully, fully justified and I agree... That's not what I want.
...
When I say "co-op option in my singleplayer game"... It is meant as a fully complete singleplayer game... Just as we normally play them. With full immersion into it and what not...
It just has the option... of bringing a friend along in some way, to enhance and share your experience.
It reaaaally hasn't been done before in the way I imagine it...
Here's a few examples of the way(s?) I imagine it:
Imagine me3 singleplayer and you're doing a mission. You're new at the game and/or it's on a hard difficulty and your ai companions are... well ai... so you could use a little bit of help. Invite a friend who's more experienced. Let them take the place of one of the NPC's and help you out in the battle.
Imagine a mass effect game. Everythings the same, but you have the option of bringing a "personal aide" (for lack of a better name, the 2nd player character) along for missions and running around citadel and normandy.
You're still the commander and you still interact with all the npc's as you normally could and make decisions. You're just able to, if you so choose, to have your friend along for the ride.
To share in your experience/the story you're telling... from within the game itself.
PS: I see this as the abilitity to tell the stories we ourselves are creating in the game to another person in some other way than creating a "let's play" video. And from that perspective I think it could be super interesting.
...
Easy? No...
Without ginormous technical challenges? No...
But the point is... if it's done as I imagine it... It would not change the singleplayer experience at all (at all is a big guarantee, but lets for the sake of argument say 95 percent the same as regular singleplayer), if you don't want it... And if you want it, it can enhance your experience.
...
And again... if it fundamentally changes the singleplayer experience... then it's not the co-op / mp / whatchamacallit im talking of and I agree completely with the opposition against it.
PPS: Tho I do enjoy me3 mp alot... But thats something entirely different and deserves to be distinctly different.