After exchanging skittish hellos, they decide to kill some time together before Jesse has to head for the airport to go home. Like the earlier movie, “Before Sunset” turns into an orgy of talk—flirtatious, soulful, boastful, self-deprecating talk, some of it borderline pretentious but all of it utterly convincing as the kind of intelligent and foolish things said by people who connect with each other through their tastes and their passions. “Sunrise” was fresh and easy and ardent. This movie is enchanting, too, but it goes deeper; it’s more direct, with intimations of sharp disappointment and unhappiness. Linklater wrote “Sunset” with help from the two stars, and one of the insights developed in the script is that most of us only get hungrier as we get older—more eager for experience, for emotional danger. Jesse and Celine are still a romantic possibility.

He then mentions a link with Rohmer which I find myself very interesting:

People who long to hear good conversation in American movies often wonder, Where
are the equivalents to an Eric Rohmer movie like “Claire’s Knee”? Well, Linklater, the movie kingpin of Austin, Texas, who earlier made the cult classics “Slacker” and “Dazed and Confused” and, more recently, the commercial hit “School of Rock,” has now created two such films. This one is both more spontaneous than Rohmer’s work and more daring in its technique. “Before
Sunrise” was a night film; Jesse and Celine sampled the miscellaneous pleasures of the street, talking to strangers and performers and whoever else couldn’t get to sleep. The new movie is set in a sunshiny late-afternoon Paris. For long
stretches, the couple walk through the labyrinthine Latin Quarter, with its yellowish-gold walls and tiny shops, and then through the winding paths of an elaborate garden nearby. As they move, the camera calmly recedes before them.
Linklater’s technique is simple and straightforward yet completely successful as a way of inducing the awkward self-revelation that he wants from his actors. Some of the shots seem to last forever, and the lengthy takes allow us to see the moments of hesitation and retreat and lurching breakthrough: when Jesse and Celine reach boundary lines—should they say what they really feel?—they take a deep breath, pause, and abruptly plunge into candor. The drama of the movie emerges from its form: “Before Sunset” plays out in real time. (...)

About the two actors/ characters physical changes:

In the earlier movie, Ethan Hawke had the soft mustache and goatee and flowing hair of a Renaissance poet. After nine years, he’s lost some of his youthful beauty. The hair is clipped; the beard now seems sparse and raffish. Lean and pale, Hawke is only thirty-three, but he’s got the harrowed look of one of those
downtown artists who work and drink too much and sleep too little. As Jesse, he doesn’t give a large-scale performance, but he catches a few small things beautifully. Jesse is still boyish, in the American way, wrestling with how much ego to show. He’s proud of his book but self-mocking at the same time, and he speaks haltingly, and then in spasmodic bursts. We can believe him when he says he doesn’t find writing easy.

Julie Delpy has lost something, too—the look of a golden-haired fairy-tale princess which she had in “Sunrise.” Her features no longer have that plush, rounded softness, but, as she has gained in definition and intensity, she’s become even more attractive.

Delpy was born in Paris, into a show-business family, and she has made films with Godard and Kieslowski, yet she doesn’t project the intimidating self-sufficiency characteristic of so many French actresses. She has spent a lot of time in New York (she graduated from the N.Y.U. film school in 1996), and she
has a partially Americanized sensibility. There’s something tentative and exploratory about her, an eagerness to try out an idea or an attitude, which Linklater tenderly draws on. In both movies, Delpy brings to the deep-dish conversations about life and love a charge of apparent artlessness: she seems to be discovering her emotions as well as her ideas as she goes along, and when she’s abashed by how much she feels she laughs at herself before giving in to emotion once more. From the first moment in the bookstore, Celine is trying to fascinate Jesse all over again, to seduce him with her melancholy, her neurotic difficulties in love. She wants attention from men, she says, but when she gets it she feels like she’s suffocating. What could be a greater come-on to an aesthete like Jesse? The couple are aware that their story is still a fable. “Before Sunrise” and “Before Sunset” are a rare case of two movies that rightfully demand yet another sequel.