These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Fridge Brilliance: Sir Robin finding his grail in musical theatre becomes this when one realizes that the actor who played him in the original film — Eric Idle — is the librettist/co-composer of this show.
Genius Bonus: Patsy saying he's Jewish on his mother's side. According to Jewish tradition, your Jewishness is passed matrilineally (i.e. you're a Jew if your mother was Jewish), so that's the only way you can be Jewish.
You technically can be Jewish through your father's side, but it's a lot more work and there is a test. It's practically the same as a non-Jewish person converting, just slightly simpler.
The Lady of the Lake's "Diva's Lament" originally included the lyric "I've no Grammy, no reward/I've no Tony awards!" Sara Ramirez then proceeded to win the Best Featured Actress Tony for the role of the Lady of the Lake, requiring the change to "All our Tony Awards/won't keep me out of Betty Ford's!"
One-Scene Wonder: John Cleese, despite appearing only as a vocal recording, does a very amusing performance as God.
One scene near the end has two: Tim the Enchanter and Brother Maynard.
Visual Effects of Awesome: The Black Knight scene used brilliant effects and visual trickery in the dismembering of the titular character.
By costume design standards. The lady of the lake was able to transform her huge magical blue gown into a completely different white wedding dress, seamlessly, on stage, without moving, in a split second.