People made fun of Guitar Hero because it made people who had no musical talent pretend that they did. Before that was Dance Dance Revolution, which didn't really involve any dance skills, but some of the more hardcore players drew in a captive audience regardless.
Now with Rock Band, a combination of vocals, guitar, and drums, you can have your very own band without much musical talent at all and people will definitely be mesmerized. However, you can't be completely tone deaf if you want to sing, and the drums is actually kind of hard. We played Rock Band throughout the entire Thanksgiving weekend and the only person who nailed the drum portion was actually a drummer... in a real band.
Rock Band is a way for people to bond and have fun together. With my brother on drums, my husband and sister on guitar and bass and me on vocals, it actually felt like we were working together. We had to, because each member has to pull their own weight to get through the song.
The downside is that the Rock Band guitar was poorly made. If you thought the Guitar Hero guitars were bad, the buttons became unresponsive after a few hours of play. We have already put in an order for a replacement guitar.
The hefty price tag is another issue, but with some friends you'll definitely get your money's worth. We hosted Thanksgiving and had over 30+ people over and it was something that people actually sat around and waited to have a turn. (We had other game stations set up, like Wii, poker, board games etc.)
So if you haven't had a chance to try it yet... run out to Best Buy, I'm sure they have it set up. :)