Henry V and Private Lives
Henry V at the Exchange is a terrific production in a unique and fascinating space, probably the most convincing Shakespeare in the round I've seen (though Epstein's Lear in a ruinous BU office building that was soon to be remodeled was very fine, too)
But Noel Coward's Private Lives and the Library was amazing. You read about nights like this, nights when everyone just hits their timing perfectly. At one point, two divorced lovers just looked at each other — they were talking about an old fight back when they were married, interrupted by their French landlord — they just looked for a second and the entire room erupted in laughter. It's not even a joke (and the show has plenty of them), but that's the way it worked.