I'm not entirely clear on the story, but apparently EA liked something they saw in L.A. Noire, and made us a pre-release gift of Rock Band (pre-release only in Australia; it's been out for ages in the U.S.). Drumkit and guitars now take pride-of-place in front of the big screen in the lunch room, and people gather to play during lunch and after work every day. The batteries in the guitars were flat by the end of the second day, and one guitar has already been glued back together!
Rock Band is just awesome fun. Its real value comes, of course, from playing in a band. The independent difficulty levels means anyone can join in and have a go and contribute something, even singing (if you're brave enough :) ), and it rivals or surpasses the Wii for sociability - imagine a crowd of people gathered around after work with beers, watching and talking and taking turns playing. I wonder how long the novelty will last, but it's great so far.
I'm hooked on guitar. I'm not even any good - only played Guitar Hero once 'round at Brett's place before - but I love it. I know it seems silly, but the game is fantastic at making you feel like a god when you get a good solo, even though you know it's a plastic toy guitar with five fret-buttons (well, ten if you count the high frets at the base of the neck, used for crazy solos at the end of a song!). It's especially satisfying if you know and love the song and shiver in anticipation as your favourite chord progression comes up :)
I know I don't have the motivation to learn a musical instrument properly; Rock Band provides instant, gratuitous gratification :D