"Ricki and The Flash" may not be the most complex or demanding film of 2015, and it may not be the deepest, but, in terms of the unadulterated buzzy joy and comfort it evokes from every frame, there will likely be few that match it. Director Jonathan Demme (2008's "Rachel Getting Married"), screenwriter Diablo Cody (2011's "Young Adult"), and star Meryl Streep (2014's "Into the Woods") are each near the top of their respective fields, and they come together here for what works concurrently as a poignant family drama, an incisive, frequently biting human comedy, and an infectiously soulful concert musical. Though the picture runs an appropriate but fleet 102 minutes, one cannot help but wish it would keep going—and then go a little bit longer after that.

Twenty-plus years ago, Ricki Rendazzo (Meryl Streep) went by Linda Brummel. She was a wife to Pete (Kevin Kline) and a mother to three young children, but at a certain point she could no longer deny her true passion to be a musician. She left her family behind in Indianapolis for the starry lights of L.A., released one solo album, and now, in her sixties, sings nightly at a San Fernando Valley bar with her trusty cover band The Flash. Ricki may not have much money—she also works a day job as a Total Foods checkout clerk—but she's not unhappy with the life she has made for herself. When Pete calls to inform her that daughter Julie (Mamie Gummer) is not taking well the news of her impending divorce, Ricki makes the trip east to be there for her. A lot has changed in the intervening decades—Pete has remarried Maureen (Audra McDonald) and now lives in a spacious, upscale estate—and Ricki's grown kids continue to harbor resentments over her abandonment. As she gradually reconnects with an emotionally ailing Julie, Ricki must face up to the tough decisions she has made and try to make amends as best as she knows how.

"Ricki and The Flash" thoughtfully sees its title protagonist's choices as neither admirable nor inexcusable, the actions of a woman who loves her children but couldn't bear to let her personal dreams pass her by. She didn't mean to be gone for such long stretches as they grew up, but that is how it ultimately played out once Pete remarried someone who could be there for them every day and she was seemingly no longer needed. Ricki is aware of the double standard of her circumstances, where it is more socially acceptable for fathers to leave home and aspire for more while mothers who do the same are seen as virtual pariahs, but the guilt is still always there, and it is a part of who she is and why she has never committed to her patient lead guitarist and sort-of boyfriend Greg (Rick Springfield).

Meryl Streep is a chameleonic force of nature in every role she inhabits, and Ricki Rendazzo is no exception. Able to turn the most seemingly minor gesture into a direct channel to each character's soul, the actress paints Ricki—a hippie Republican—with contradictory shades that speak to her Baby Boomer generation and free rock-'n'-roll spirit, the two halves colliding into a fully formed, entirely real person. Whether she is on stage, belting out a playbook of cover tunes with her guitar in hand, or navigating a return to her past with which she frequently clashes, Streep makes her character readily inviting and enticingly multifaceted. Her love for her kids is never in doubt; she's simply had a difficult time being a consistent presence in their lives. Mamie Gummer (2013's "The Lifeguard"), Streep's real-life daughter, comes into her own here like never before; her take on Julie, a young woman distraught over the end of her marriage and in need of someone other than a therapist to level with her and listen, feels wholly lived-in and alive with inspirations both comic and intimately potent. It is an exquisitely modulated performance, and Julie's wildly unkempt hair at the onset mixed with her unfiltered wild-card of a mouth assists in making her a true original (and, often, enormously funny). That Streep and Gummer are mother and daughter off-screen only makes their chemistry on it all the more palpable.

There isn't a weak spot among the supporting cast. Kevin Kline's (2011's "No Strings Attached") part as Ricki's ex-husband Pete isn't particularly showy, but he effectively conveys the upstanding stability and conflicted unspoken feelings of a father who was left to raise his children after the woman he still very much loved was no longer there. As Greg, Rick Springfield is a standout as Ricki's devoted bandmate and beau, the two of them bonding in their choice of profession and in the similar interpersonal sacrifices they made to get there. Springfield's actual career as a musician (is there anyone who hasn't heard "Jessie's Girl?") lends Greg a further authenticity, but it is his naturalism and compelling dramatic chops off the stage where he truly impresses. Sebastian Stan (2014's "Captain America: The Winter Soldier") and newcomer Nick Westrate exhibit the subtly disparate relationships two siblings close in age can have with the same parent as Ricki's sons Josh and Adam, the former engaged to Emily (Hailey Gates) and the latter having recently come out. As bartender (and resident Ricki groupie) Daniel, Ben Platt (2015's "Pitch Perfect 2") is disarmingly sincere and unabashedly charming.

Finally, Broadway staple Audra McDonald (2003's "It Runs in the Family") threatens to steal her scenes as Pete's current wife Maureen, going head-to-head with Streep in a bravura sequence where they confront the long-simmering contentiousness between them. Maureen could have easily been written as a one-note, humorless construct, but Diablo Cody refuses to see her that way. As the woman who helped to raise her stepchildren after Ricki left, she is given a point-of-view as valid as it is understandable. Maureen arguably knows Julie, Josh and Adam better than their birth mother does, and this realization stings Ricki more than words ever could. McDonald is exceptional in the role, and blessedly not without empathy.

"Ricki and The Flash" is unforced and vibrant, and just as he did with previous feature "Rachel Getting Married," director Jonathan Demme tells his story with a free-floating, slice-of-life looseness that allows the characters the chance to breathe. The story is consistently moving forward, to be sure, but it unspools in a way that never feels manipulative or labored. And then there's the music! Kicking off with Tom Petty and the Heartbreakers' "American Girl" during the opening credits and following that up with tracks from the likes of U2, Bruce Springsteen, and Lady Gaga, the song performances (recorded live during filming) prove ridiculously thrilling to behold. An early scene where Ricki strums to her original song, "Cold One" (written by Jenny Lewis and Johnathan Rice), is beautiful, the viewer as enraptured as Pete and Julie. The biggest highlight, though, is Streep and Springfield's cover of Dobie Gray's quixotic "Drift Away." That this performance is allowed to play out in full, speaking volumes through the lyrics, the vocals, and the actors' clear exuberance and love for the music, makes all the difference. The electricity of this three-and-a-half minutes of film elicits legitimate goose chills. Taking a page from 1987's "Dirty Dancing," the somewhat similar finale is full of such warmth and good spirits that it hardly matters if the particulars of what is happening are potentially contrived. By this point, the movie—and everyone involved—have earned a happy ending. There are many reasons to gush over "Ricki and The Flash," but at the top of the list is Meryl Streep. She was born to play the brassy, vulnerable, endlessly fascinating Ricki Rendazzo. The fun that comes from getting to watch her do it for a couple hours is, frankly, preposterous.