Paul is so loose and animated. Fantastic. Man they looked like they were having a ball.
I'd say that is one of the things that made them so exciting and popular at the time. Not many bands in those days having fun on stage and performing with so much energy. Even during their last show on the rooftop they seemed to be having a blast.
Here's a few more examples:
"I'm Down" on the Ed Sullivan Show:
And the classic example of out of control exuberance, "I'm Down" at Shea Stadium (snippets only):