Greatness is determined not only by success, but also largely by the manner in which that success is achieved. In other words, STYLE is an important aspect.
This applies to all sports, not just tennis. (eg. Brazil 1970 are a GREAT football team, Italy 1982 are not GREAT.)
Actually, reading that back, I guess it won't be that unpopular with many people here...
Winning IS winning, no matter what the style of play. I prefer Federer's style to Rafa's but would rather have Rafa's H-H against Roger. I like Guy Foget and his game, but the fact that he May have had a better volley than Sampras of Becker in irrelevant, in that he didn't win many tournaments with it. I find it pathetic that some, mostly Federer fans, can't stop trashing Sampras and the great players of his era. Anyone who says 03-07 was not a weak era or Roger declined at 26, just can't handle the truth.