Why is Act 3, Scene 2 of A Midsummer Night's Dream interesting and effective?
It's the moment where Shakespeare has maximum fun with all the trouble he's set up with the lovers. Firstly you get Puck recapping what's happened with Titania and Bottom, and how he has turned Bottom into a half-donkey.
Then you get the - traditionally comic in the Roman master and servant mode - moment where Oberon realises that Puck's put the "love-in-idleness" flower on Lysander instead of Demetrius:
What hast thou done? Thou hast mistaken quite,
And laid the love-juice on some true-love's sight.
Of thy misprision must perforce ensue
Some true love turn'd, and not a false turn'd true.
Puck persuades him, though, to have some fun and watch the lovers' confusions:
Shall we their fond pageant see?
Lord, what fools these mortals be!
It's a key moment - and the climax of the lovers' plots. What ensues is a massive, passionate argument-cum-fight with the lovers defending each other, attacking each other, teaming up. It's very confusing and the high point of the play's argument that love is quite close to a sort of hallucinogenic madness. And then, right at the end, Oberon turns the play's motor towards its eventual resolution: he sends Puck to sort the lovers' enchantment out, and he himself,
Whiles I in this affair do thee employ,
I'll to my queen, and beg her Indian boy;
And then I will her charmed eye release
From monster's view, and all things shall be peace.