Since I bought Rock Band (RB) for my PS3 a few months ago, Guitar Hero 3 (GH3) grew roots on the shelf. GH3 was my first fake-music game, and I enjoyed it very much. But the same source who prodded me to try Guitar Hero implored me to try Rock Band. And sure enough, I liked it more.
The multiplayer in RB would have been enough all by itself. Having my buddy over to jam on "March of the Pigs"? My wife singing "Call Me" at the top of her lungs? All of us laughing and cursing at how hard Boston music is to play and sing? You just can't put a price on that.