Just a quick invite to those people posting about "only playing single player". Why?
I play single player, because I don't want to deal with other people. *shrug* Playing against the AI, I can get an experience that I can define myself in terms of difficulty (some days, I want a challenge, some days, I just want to kill everything in site like some outraged, vengeful... Demigod ), I never have to worry about the AI calling me names or just being an idiot, I can experiment freely without ruining the experience of other people, and I really don't care how I stack up against others (so, rankings/achievements hold no real sway for me.)
Mainly though, the annoying people I run into ruin the experience for me, even though they're still outnumbered a hundred to one by the decent people. (This is also the reason why I tend to stay in stalker mode on most well-trafficed forums.) I deal with enough annoying people in the real world; why would I also deal with annoying people in the thirty minutes a day I have to game? We spend too little time with things we enjoy, as is.
I do enjoy LAN parties, but then there's no problem, because I know everybody in the room. So, for me, multiplayer is a function of the audience, not the game.
*shrug* Don't know if I'm an outlier or not, standard disclaimers apply, YMMV. And I'm certainly not stating that my viewpoint is definitve, or even completely rational (though it's rational enough to me.) But that's why I choose to spend my entertainment time playing single player.
JGH