Cyrano doesn't even appear until about half-way through Act I, but when he does, not only does he appear from the audience (when the play is performed), but he's yelling at one of the actors to get off the stage because, as we find out shortly afterward, said actor had been hitting on Cyrano's girl. Actually...all of Act I is Cyrano's Establishing Character Moment.
The opening scene, when we find out that Antonio is chronically depressed, Salarino and Solanio are Those Two Guys who want to cheer him up, Gratiano is a party animal who constantly goes off on tangents and Bassanio is Antonio's Heterosexual Life Partner who's blown a lot of money and wants to marry the fair Portia. (Oddly enough, Lorenzo, the other guy in the scene, doesn't really get his character established until later—although he does make a crack about Gratiano never letting him speak, and later on he chastises Launcelot for talking too much, so presumably talkative people get on his nerves.)
Portia and Nerissa's first scene sets Portia's personality up for the rest of the play, besides establishing Nerissa as her best friend and straight woman.
Shylock's status as a Jew and a usurer, plus his grudge against Antonio, are set up in his first scene, when he and Antonio argue about the theological implications of usury. Plus, he makes the "pound of flesh" bargain at the end of the scene. The Character Development that turns him into an Ineffectual Sympathetic Villain—and leads to his famous "Hath not a Jew eyes?" speech—comes in dribs and drabs.
The Prince of Morocco gets his character established as a precursor to his choice of the wrong casket. Arragon's speech also serves this purpose later on, but he's only in one scene...
Launcelot. "Certainly my conscience will serve me to run from this Jew, my master!"
Jessica gives a soliloquy letting everyone know that she's Shylock's daughter, that she's ashamed to be his daughter, that she's ashamed of herself for being ashamed, that she's nothing like him, and that she's in love with Lorenzo and wants to marry him and become a Christian.
The two scenes in which Lorenzo a) sets up his elopement with Jessica and b) carries it out.
The whole of Denmark is celebrating the new king's wedding yet Hamlet is sulking in a corner wearing black because he's still mourning his father.