On the early Fed era:
From the Australian Open 2004 to the Australian Open 2009, Federer played in 25 Major Championships. He won 15 of them, made the Finals in 6 of them, and only missed the Semi-Finals once.
Maybe people think the era was weak because Federer was so much better than them that they couldn't build up their legacies. I mean, he beat Roddick in 3 Finals and 2 Semi-finals.
Lleyton Hewitt had 2 titles, and was killed by Federer-- Hewitt was beaten in 6 of Federer's titles mid-2000s. Safin had 2 titles as well. He beat Fed, like, once or twice.
EDIT: Adding in the end of Agassi's career would have stretched farther, too, and he'd have 9-10 titles. There wouldn't be much of a gap between the end of the Sampras-Agassi careers to the Nadal-Djokovic...
But if you didn't have Federer, the era before Nadal really emerged would have probably had Roddick, Hewitt, and Safin splitting a bunch of titles, and we wouldn't think about it in the same way. Fed just mowed everyone down until Nadal could regularly compete with him.