Originally Posted by whoknows
They weren't whole missions IIRC. The only parts you repeat are a couple points where you meet up with other characters and can play online with other people.
You may be in the same areas as some of the other characters in the story were/are at during certain points, but you aren't doing the same thing at all.
I agree about the playtime though. I loved that the game offered so much. Something that I would hate to see go in future games.
Yeah, some locations collide, but only for a small portion of each campaign.
For those who have not yet played the game, one way to play it is to play each campaign, finishing with Ada's (which is essential that you finish Ada's last and do indeed play through Ada's campaign).
There is another "chronological" way of playing it too, mixing the chapters.