There's no doubt about it. Arcadia is Tom Stoppard's richest, most ravishing comedy to date, a play of wit, intellect, language, brio and, new for him, emotion. It's like a dream of levitation: you're instantaneously aloft, soaring, banking, doing loop-the-loops and then, when you think you're about to plummet to earth, swooping to a gentle touchdown of not easily described sweetness and sorrow.