Hmmm...very interesting topic. While there are certainly artists/bands that I don't particularly care for, I tend to focus on the greater cause... the appreciation for MUSIC!
If I were forced to rate any artists/band (in this case under/over rated) I would do my best to skirt the issue and instead suggest that I be allowed to compartmentalize them as follows:
1. Artist/bands that understand that if you put the music first, the money will follow. These types tend to have the longest careers because they remain passionate about the creativity of music.
2. Artists/bands that for good or bad, changed the game, and either advanced music, or made us appreciate the aforementioned more; sort of like pop art. you don't have to like Warhol, Haring, or Basquiat but there is no denying that they changed the game, and one could argue brought "Art" into mainstream.
3. Artists/bands with a unique sound that cannot be duplicated. For that reason alone they deserve a spot in music history and thus should be excluded from any 'overrated' label (no pun intended). AGAIN, you do not have to like them, but on a spiritual level (if you believe in that) they have been gifted something that no one else has. Examples: Dylan, Bjork, Prince...etc.
Thank goodness 'Culture' rejects the opinions of the few ;)