It is pretty hard to state whether it is single, or multiplayer going down.
I have heard and read so many contrary opinions, pointing out so many good examples for each of the two theories, that it looks like some Godzilla-style monster fight now. Having that in mind, I will state my own conclusion, that neither is the case.
But when you think about it, you can not disregard the growing influence of Internet in daily lives of the yet un-digitalized (pre-casual?) human beings across the planet.
Furthermore, owing to party games like Guitar Hero or Buzz, the common idea who a gamer is, keeps changing (or even! I would dare say: improving).
Thus, the conclusion - multiplayer games will grow their share of the market of the global village, especially when the common idea of a hardcore single-player gamer is somewhat dramatically bound to masturbation; figuratively that is.
The issue is, however - that in popular belief, multiplayer is somehow bound to dull replayability as a must. This casts a shade on my part of the game, and strips the social part of the game from what the single player part is often firmly based on - the story.
And it is a fact, I believe - that everyone likes a story! I do enjoy consuming stories with other people, and there is no doubt in my mind, that I am not alone with such a preference.
There has been indeed a bit of motion in the topic, with slow growth of games aiming at cooperative play (but mostly in games, which would be otherwise indigestible for me - like R6:Vegas2 or Army of Two).
Yet, the potential greatly outgrows these. And I am definitely not talking about MMO’s here.
Multiplayer could use more stories.