Tough call. You really have to think about who will be playing. Younger people might not be able to grasp Rock Band, but older people might not enjoy Mario Party for AS LONG as they might enjoy Rock Band. You also have to consider you players musical interest and inclination. In my experience, I've played both games with groups of friends (college age), and we've had a lot of fun with both, but have played Rock Band more, BUT we are all very interested in music, and most play real instruments; so it's all a matter of preference. With the Rock Band having new songs (and soon whole albums) available for download EVERY WEEK, the longevity seems to be better for it (note: the upcoming Wii edition of Rock Band will not have any downloadable songs, or character creation). As much as I love Nintendo, I also love music, so if I had to pick one, it's be Rock Band (on my 360) over Mario Party 8. But again, if you or your friends just aren't into music, this could be no good for you.

If you are talkjng about on the Wii, Rock Band won't be out till I heard May. Mario Party 8 is cute and my kids enjoy it and I do play it with them but if you are talking about a group of just adults I think you'd enjoy Rock Band more. We currently have Guitar Hero for Wii and it is a lot of fun. Mario Party 8 for just all adults I think would get a bit tiresome. It is cute but not challenging or anything like that.

Not eveyone is inclined enough to play rockband/GH. Mario party is fun for those adults who used to own a gamecube and are familiar with the mario party series. My brother and his friends could play guitar hero all night with each other. Unlike my friends, who we can spend hours playing mario party.

Younger kids and older adults will enjoy MP8. Teenagers and young adults will probably prefer RB.

It all depends on who it is you are playing with. Some people are going to like Rock Band better, some are going to like Mario Party. My little girls would not like rock band, but some of the youth in my youth group would love it.