Back when I were a lad (and all this were fields and you could get into t' cinema for t' jam jar) gaming was still in the early stages. It wasn't a toddler any more but it was still bringing people together in a much more real way than it does today.
Gaming with my brother was always full of the hard decisions... and even before the dilemma of 'which sibling will get the third party controler (always the youngest) we had to decide who would get the "normal" controls on the keyboard, and who would be relegated to the keys in second place.
The younger readers here may have a slight problem computing this... but I can assure you, even in the late eighties, it was possible for two people (or more) to play a game using one television, one "console" and one keyboard. It was trickier to get four hands on and not get in each other's way, but if you wanted to game two player on an Amstrad, that's what you had to do.
Things were going so well, we evolved into the Xbox 360 and Playstation 3 having instant ability to attach four controllers... which seemed great, but where the hell are the games? Sure if you want online co-op or deathmatches, we're pretty sorted. But what about when me and the almost wife (one week today) want to have a break and game together when she gets a break from Indy-Plays, or have a party with friends all playing together?
Again, we don't really want to constantly be in deathmatches, but it's very rare these days to find a good game which will let you go through the story mode as a two or four player unit (even some which provide online co-op). We're currently going through one of this month's Free with Gold games, Army of Two III and it's good, cooperative play. We've gone through Lord of the Rings titles which were ok and, of course, Borderlands. All of these were ok when playing single player, but I will always enjoy a game more when I can play it with friends, and as I live with my best friend, I want to be able to play with her too!
Looking at the listings at Co-Optimus, it seems these days though, that the 'Couch Multiplayer' is a beast which is dwindling to extinction, and that makes me a little sad. Still, we definitely enjoy the ones which do support local campaign co-op via splitscreen, even if we are a little limited by what we can choose.