A Midsummer Night's Dream
Four lovers flee into a wood outside Athens and wake up wrong: the fairy king is feuding with his queen, a mischief-spirit is dosing sleepers with a love-flower, and a weaver named Bottom is given the head of an ass and the affections of a goddess. It is Shakespeare's most perfect comic machine, three worlds — court, fairies, amateur actors — interlocking without a wasted scene. Underneath the moonlight it asks a genuinely unsettling question: if love can be switched by a drop on the eyelids, what was it before? The rude mechanicals' play-within-the-play is still the funniest thing he ever wrote.
The lovers are interchangeable on purpose, which is the joke and also the problem: two acts of Lysander and Demetrius is two acts of the same man arguing with himself. The frame plot hands Hippolyta to Theseus as a war prize and never looks back, and Oberon ends the play having drugged his wife into loving a donkey and won custody of a child by it — a resolution the moonlight is doing a lot of work to soften. Delightful in performance; on the page, the machinery shows.
The case for it and the rest of the canon open with Pro.