One thing cool in the Get Back docu was seeing the Beatles break out into snippets of old blues or rock songs or even the very early Beatles songs. Those voices and instant harmonies.
@hawaiiboy Lennon & McCartney's skill at harmonizing was amazing. I always hold up "She Loves You," a song I don't otherwise especially like, as an example.
@JMaxB great example. Their musical chemistry is astounding, even when they are especially getting along.