We can never really tell how great Schumacher was or wasn't as he and the teams he drove for consistently cheated in every possible way throughout his period of winning.
It could be a clue that when he came out of retirement and drove a Mercedes, built to the same rules as all the other cars he was a mediocre, bad tempered midfield driver.
Personally I don't just measure greatness by results. I will maintain to my last breath that Gilles Villenueve was the greatest driver there has ever been, closely followed by Senna. Villenueve won a handful of races and no championships in his short F1 career.
Having watched Hamilton since his days in GP2,I think I might have to put him in the number 3 spot.
He has a level of talent and commitment that mere mortals can only dream about imho.
Apparently there is a programme (or part of one) about Villeneuve on SKY F1 tomorrow before the race.