So, it's been more than four months since Rock Band came out - there's not a lot I can say about the game itself that hasn't already been said. Best multiplayer in-person game ever made, blah blah blah.
But four months later, I play Rock Band more than any other game I own. Rarely a week goes by without a couple games or Rock Band with other people, which means that almost every week since the end of December, I've been playing a game with a friend, in person, every week.
Rock Band's almost like a social "endcap" to an interaction. Brunch ends with a game of Rock Band. Dinner, then Rock Band. An afternoon get-together -> Rock Band. Almost everyone I know has played it and enjoyed it. People I would never have thought would sing, sing. People I would never have thought would have any rhythm play drums. The cooperative nature of it prevents newbies from feeling incapable, and there's enough levels of difficulty that even four months later, I can have a nice challenge while playing with someone who's never played before.
So it's a great game - but that it's become such a part of my social landscape is unusual, and that it's become a regular experience for so many non or casual gamers is astonishing.
Would that every game were this good.