Former SNL "Weekend Update" co-anchors Amy Poehler (2014's "They Came Together") and Tina Fey (2014's "This Is Where I Leave You") are such effortless screen partners it is hard to believe "Sisters" is only the second film they have headlined together, after 2008's "Baby Mama." If the finished product cannot match the sky-high expectations fans have built up over the last seven years, seeing them reunited--and as total-opposite siblings, to boot--hits the sweet spot. There is a bit of a scattered feel to this up-all-night, cameo-filled party farce, as if director Jason Moore (2012's "Pitch Perfect") and writer Paula Pell (TV's "Saturday Night Live") have seemingly tossed everything they could think of onto the ceiling in hopes it sticks, but its heart is strong, its messages affirming, and its mélange of acerbic humor delivered with relish.

Maura Ellis (Amy Poehler) is a do-gooder nurse, responsible to a fault. Elder sister Kate (Tina Fey) is an impulsive, recently fired beautician and single mother whose teenage daughter Haley (Madison Davenport) has begun to pull away from her. When retired parents Bucky (James Brolin) and Deana (Dianne Wiest) announce to Maura they are planning to downsize and move out of their family home, they convince her to lure Kate to Orlando so they can clean out their childhood bedrooms. Kate initially doesn't take the news well, then formulates a crazy idea: invite all of their old high-school classmates over for a throwback blowout bash. For Maura, who has always lived her life on the straight and narrow, it is a chance to finally let loose the way she wished she had when they were teens. A flirtatious encounter with nice-guy handyman James (Ike Barinholtz) also could mean something more: finally moving on after a tough divorce.

Top to bottom, "Sisters" features such an extraordinary cast of often overlooked or underused actors it comes as both a treat to see them and a letdown that many of them, once again, get little to do. Of the ensemble, a likable, down-to-earth Ike Barinholtz (2014's "Neighbors") and an amusingly scorned, then spiteful, Maya Rudolph (2013's "The Way Way Back") get the best supporting roles as, respectively, Maya's love interest James and Kate's high school frenemy Brinda. Others, like Rachel Dratch (2012's "That's My Boy") as a friend going through a midlife crisis, John Leguizamo (2014's "Chef") as a skeevy guy from school with boundary issues, and Heather Matarazzo (2007's "Hostel: Part II") as a pal of Brinda's ready for more excitement in her life, are mostly there as window dressing.

Jokes are hit and miss in "Sisters," but Amy Poehler and an against-type Tina Fey carry the part-raucous, part-slice-of-life nature of the script with ease. One cannot argue too much, anyway, with a film meant to be a good time and not much else. A scene set in a nail salon where Maura desperately tries to pronounce manicurist Hae-Won's (a very funny Greta Lee) name goes on and on, escalating in hilarity with each passing second. There is also truth in the film's look at how fleeting the frivolity of youth can be, and how easier said than done it is to recapture that feeling. There is a great gag where Maura and Kate fool a cop into believing they are holding a wake inside the house based on the guests' looks of defeat and sadness he glimpses through the window. Eventually, though, everyone does let loose in a way they haven't for years and may never again. And then things get really out of hand. As Maura and Kate learn about themselves and come of age (twenty-plus years late) in different ways, they say good-bye to their childhoods but earn something better, both apart and as siblings and friends. "Sisters" is narratively gangly, but the movie's energy and the actors' enthusiasm rarely flag. For the span of two hours, the fun they're having is infectious.