He's the best plexicushion player ever obviously, but I'm not sure I can rate his 3 in a row over Federer's longevity when considering the rebound ace era. 10 semi finals in a row, an extra final appearence and the same number of titles is an impressive record. Agassi also would have won more if he played at the AO more as well. I feel like part of the reason some are eager to anoint Nole as the AO GOAT is because they expect him to rack up a few more titles there. Which no doubt he will.
I'd say with respect to Agassi and Federer, Djokovic is only on their level. He will surpass them by leaps and bounds though IMO.