I thought it would be fun to see what people chose as highlight moments from the three episodes. I titled it spoilers so if people don't want to know everything that goes on they can wait til they've seen it.
OK I'll lead off with some off top of my head:
Paul referring to George's Hare Krishna friend, who was sitting quietly in the studio, as very clean.
Paul asking John if he's written anything more and Michael Lindsay Hogg getting the large boom mike above them to capture the interaction, with John and Paul then acting it up for the cameras
George's boots in episode 2
Georges suit in Episode 3
Paul showing them Let it Be
Paul showing them Get Back
Paul showing them Another Day
Paul showing them Back Seat of My car
Paul showing the young guy how he writes.
Mal's joy at playing the anvil for Maxwell
John teasing Heather about eating cats
The studio staff commandeering their instruments when the Beatles had gone and trying to play something.
Ringo replying laconically when asked if he liked India "not very much no."
Billy Preston pretty much every time he's on camera.