Diana Ross only got to be the front singer in the Supremes because she was schtupping Berry Gordy. Mary Wilson was better looking and had a better voice but Gordy gave his bird the gig. The In-laws went to see Ross a couple of years ago and said she was either pissed or stoned and was so bad they walked out. She is a superstar, no doubt, but not a very good singer IMO.
Coldplay, that singer's voice drives me round the ****ing bend, it's like he's got a droopy mouth or something. Radiohead are better IMO because at least they're changing their sound and adapting each album - it doesn't always work out (their most recent album being a prime example), but something like In Rainbows (one of my favourite of all time), is really just a fantastic album that's something a little different to other bands.
Actually, now that Ive thought about it more, for sheer over-ratedness it has to be the jimi hendrix experience.