You can always recognize Wilde by his epigrams – succinct, witty, paradoxical sayings. Like this one (no offense, rock stars): "Musical people are so absurdly unreasonable. They always want one to be perfectly dumb at the very moment when one is longing to be absolutely deaf" (2.191). Fabulous. Even on his deathbed, the Wilde was funny (see "Trivia").
Most of the characters get to shoot off a few of these epigrams, no matter how they might otherwise seem. How awesome would parties be if everyone were truly this witty. Only ultra-serious Lady Chiltern scores low on the epigram count.
On the melodramatic speech count, however, Lady Chiltern scores high, as does Sir Robert. Lord Goring scores high in both kinds of language. How do we know it's melodrama? Keep an eye out for repetition, reversed word order, and exaggeration. Sir Robert squeezes all three into these words to Lady Chiltern: "All sins, except a sin against itself, Love should forgive. All lives, save loveless lives, true Love should pardon" (2.311). He even throws in a little mid-sentence capitalization for emphasis. You go, Sir Rob.