^^
You have to watch it after enjoying some 420, without that it isn't the same...
No, not at all. You're confusing smart comedy with some abstract psychedelic bullshit like Eraserhead, Fear and Loathing, Into the Void, The Wall, etc. More visceral stuff.
In fact, Grail has way too much subtlety and nuance to fully appreciate stoned. All Gilliam's films are fairly sophisticated that way (except maybe Time Bandits).