By now, there have been enough comedies about pregnant teens that it could almost become a subgenre in itself. While "Juno" is not exactly novel in its subject matter—it holds a similar acerbic wit to two previous movies of its ilk, 1998's "The Opposite of Sex" and 2004's "Saved!"—it plays its familiar cards just right. Sweet without being mushy, very funny without needless over-the-top histrionics, and smart enough in its story turns and characterizations to put to shame most dumbed-down Hollywood filmmaking, "Juno" is 92 minutes of unforced, undemanding bliss.

Ellen Page (2006's "Hard Candy"), racking up quite an exemplary résumé for herself, is perfectly cast as 16-year-old Juno MacGuff, a self-deprecating know-it-all who finds that there's a lot she doesn't know when she gets pregnant. Well aware that she and the would-be father, classmate and best friend Paulie Bleeker (Michael Cera), are ill-equipped to even consider raising a child, Juno comes clean to patient father Mac (J.K. Simmons) and dog-loving stepmother Bren (Allison Janney) and then promptly announces that she wants to give the baby up for adoption. The prospective parents she chooses are Vanessa (Jennifer Garner) and Mark Loring (Jason Bateman), a well-off married couple who, at least in Vanessa's case, are delighted yet learned enough in adoption matters to not get their hopes up. As Juno's first trimester becomes her second, and then her third, she faces some tough decisions when she learns that Mark isn't as gung-ho about be a father or a husband as he initially let on.

Nicely directed by Jason Reitman (2006's "Thank You for Smoking"), "Juno" is light on plot but plentiful in moments of keen human observation. The screenplay by former stripper Diablo Cody is impressive for a first-time writer, and is destined to make her a hot commodity. The characters she has created are not types, but clearly defined and fleshed-out individuals, and the dialogue she has written for them pops with electricity and bite. Cody sprinkles in a fair share of pop-culture references, but they derive naturally rather than as a ploy for being hip, and there are some clever barbs directed at, of all people, Diana Ross and Soupy Sales. A few side details threaten to become overly precious, such as Juno's hamburger phone and preference toward blue raspberry Slushies, but they hold no bearing on the film's all-important heart.

There are times when the viewer can sense manipulative story developments are only a stone's throw from revealing themselves, but these predictable and condescending episodes refreshingly never take place as expected. The film is too intelligent for that, and so, when Juno starts hanging out with Mark while Vanessa is out of the house, trading music and watching Herschell Gordon's "The Wizard of Gore," what one thinks is going to happen goes in a different and altogether more organic direction. The tone of "Juno" is light and playful, but not above the reality of its situations. When it ventures into darker contemplative areas, the drama within these characters' lives and circumstances rings as true as the underlying humor does. It helps that writer Diablo Cody obviously loves her characters as much as the audience grows to. Kudos, too, for penning a teenage girl who shares a solid relationship with her parental figures, rather than a pent-up and angry one.

Ellen Page is a one-of-a-kind young actress who, like many of the roles she portrays, seems to be wise beyond her years. She is not a model or a stick figure or a blonde bimbo, but an earthy, somewhat quirky, beauty whose presence onscreen is invaluable. Sarcastic without being bratty, honest without being snooty, worldly but not without a speck of naiveté, Page turns Juno into a lovely, rough-around-the-edges original. As Paulie Bleeker, Michael Cera portrays what feels like an extension of the character he recently played to much acclaim in "Superbad." Cera's awkward adorability is just that, and it will be interesting to see the trajectory of his acting career as he branches out into different kinds of parts. Supporting performances are strong across the board, from Jennifer Garner's (2007's "The Kingdom") vulnerable Vanessa, so impassioned about finally becoming a mother, to Jason Bateman's (2007's "The Ex") stunted Mark, clinging to a probably fruitless dream of emulating the rockers he has grown up to adore, to J.K. Simmons (2007's "Spider-Man III") and Allison Janney (2007's "Hairspray"), warm and relatable as Juno's dad and stepmom.

Scored to a compilation of deliciously peculiar but catchily melodic songs by Kimya Dawson and Matt Messina—they are as close as the film gets to a Greek chorus—"Juno" is a comfortable, likable, down-home slice-of-life. The love story that evolves between Juno and Paulie could have afforded a few more scenes to display exactly what it is each of them see in the other, but then again, both characters are innately good kids impossible not to be endeared by. As the simple story of a young woman coming of age in ways that she never could have envisioned for herself, "Juno" is authentic and, oh, so winning.