My friend Steve said once, "Everyone likes Coldplay, but you don't ADMIT that you like Coldplay."
Much truth to that. Clearly, there are many other bands that are more mainstream and banal, but Coldplay is the quintessential example of a band that is so adept at crowd-pleasing mediocrity that what they end up with is music that everyone seems to like and can't really complain about, but it's music that really isn't interesting or outstanding in any way. The very definition of mainstream.
In today's New York Times, Jon Pareles goes even further, calling Coldplay "the most insufferable band of the decade":
http://www.nytimes.com/2005/06/05/arts/music/05pare.html?pagewanted=1&th&emc=th Now ... what am I going to eat for lunch?