Mass Effect 3 should have a multiplayer. It does fit. Though, instead of co-op, I'm thinking maybe they should do normal competitive-type multiplayer gameplay, Shepard v Shepard, or make your own character, with multiplayer-unique abilities, leveling up as you play.
Assassins' Creed Brotherhood: COME ON! 'Whodunnit' scenarios! Think about it!
Oddworld: Abe's Exoddus (I think Oddysse did too) shouldn't have, it was really awkward. Horror games, I totally agree on. Remember Resident Evil: Outbreak 1+2? Silent Hill, definitely. Dragon Age, meh.