Man is that a subjective thing! For me the ability to convey the emotional impact of the lyrics is key to a great singer. Bob Dylan does not have a great voice in my opinion but damn it, when I listen to his songs I am enrapt by the emotions. Secondly, they have to be convincing . In that I mean they have to convince me that they believe in what they're doing with the song and their music. We have all heard "musicians" and "singers" who are technically credible but you can tell they're just there to collect the loot promised them. (Somebody mentioned the Spice girls and I would add Brittney(SP) Spears et al.) The late Eva Cassidy is a good example for me of a great singer. there is raw power and emotion in everything she does. The only song of hers I haven't found convinciong is her cover of "Over the Rainbow" Aretha Franklin and Lucinda Williams have that raw power and emotion in their works also. But again, it is subjective and that's what makes these discussions such fun. Kindest regards, neil