The shirtlessness and overt intense sexual aura adds authenticity, and ushers in the era of sex in music, which would be furthered by the Doors, David Bowie, funk, punk rock, heavy metal, and now almost every other act in music today.
In other words, this concert movie isn't great because it documents the presenting of new sounds or new music to the world, after all, these songs are all about a decade old, but it is a great movie because it documents the presenting of a new mood, a new philosophy, or maybe an old one. It documents a new naked unabashed style of performance, and the lifting of previously banned or unacceptable themes, like lurid staring, and a shirtless male beckoning the crowd like a lover, and a black man embracing his sensuality in a room full of admirers, and heightening it even further.
Recorded three years before the mind-shifting, ethos-shift that was the Woodstock, Festival of Peace and Love. I mean, he's literally making the crowd beg for him to throw out to them his sweaty shirt for a minute or two. The energy is insane. The music is great. The band is on point. The performer is a demon. And the crowd is perfectly in tune with the times. Great document.