Comedy trio The Lonely Island rose to fame through a series of "Saturday Night Live" numbers, including "Lazy Sunday," "I'm on a Boat," and "Dick in a Box." Then came a string of musical comedy albums that boasted appearances from Michael Bolton, Justin Timberlake, Natalie Portman and Lady Gaga. Now, the Lonely Island movie "Popstar: Never Stop Never Stopping" combines the group's love of pop culture, musical parody and celebrity cameos into a mockumentary morality tale, marked with hits and misses.

Fittingly fronted by The Lonely Island's most famous member, "Popstar" has Andy Samberg playing the egomaniacal singer Conner4Real, while the comedian's Lonely Island partners Akiva Schaffer and Jorma Taccone (the film's co-directors) co-star as Conner's shafted former boy-band mates, The Style Boyz. It's your basic "Behind The Music" narrative: Three childhood friends who come to fame together, are torn apart by greed, only to learn money can buy a lot of things -- including a personal bagpiper player for elaborate pet funerals -- but friendship is priceless. The plot is predictable and paper-thin, yet the premise gives rich opportunity to gleefully lampoon celebrity culture.

Justin Bieber is the unspoken muse of this movie, mocked in everything from the film's title (cribbing off the Bieb's 2011 concert doc "Never Say Never") to raunchy bits inspired by his infamous visit to the Anne Frank house, his "SNL" parodied modeling stint, and his nude photo scandal. But The Lonely Island also folds in jokes about boy bands, activism pop (looking at you Macklemore!), social media marketing and EDM. Even if you don't get the real-life root behind "Pop Stars" gags, there's enough straightforward silliness to thrill.

The sprawling cast is stacked to the rafters with music luminaries and comedy stars. Usher, Mariah Carey, Carrie Underwood, Seal, Pink, Adam Levine and many more appear in wry talking heads and loony performances, while "SNL" alums like Will Forte, Tim Meadows, Maya Rudolph and Bill Hader pop in for quick comedy cameos. Lesser-known but nonetheless hilarious are Edgar Blackmon and James Buckley (of the UK comedy series "The Inbetweeners") as a pair of ultra-hip Yes Men who communicate most often in overeager nods and slightly terrifying grins of enthusiasm. However, the standout cameos come from Will Arnett, Mike Birbiglia, Chelsea Peretti and Eric Andre in a scathing sendup of "TMZ," where the foursome play ghoulish cackling caricatures of the gossip-gargling reporters. Most appearances are brief to blink-and-you'll miss them. Yet "Popstar: Never Stop Never Stopping" works best when it's racing, setting up one biting bit after another.

Fittingly the musical's brightest aspects are the songs. Whether Conner is calling The Mona Lisa a "basic bitch... piece of shit" or spinning his own "Super Freak" take about a girl whose kink is cosplaying as Bin Laden, The Lonely Island nails its big musical numbers, delivering hysterically irreverent lyrics with the showmanship of a big-ticket concert. Conner4Real's songs in full swing are so funny I literally howled with laughter.

Clever in its celebrity culture satire, and outstanding in its musical comedy, where "Popstar" falls flat is in the actually being a movie bit. Its simple paint-by-numbers plot could have been made engaging with dimensional and charismatic heroes. Regrettably, Samberg, Schaffer and Taccone seem more concerned with spreading the wealth of punchlines than they do shaping their characters. Kid Brain (Shaffer) isn't carved out beyond being bitter and vaguely into woodcarving. Kid Contact (Taccone) is introduced as the insightful one, but when a scene drag he's the first to spout out a clueless comment. Without investing the audience in these Style Boyz, Conner's big emotional finale falls frustratingly flat.

The Lonely Island is masterful in sculpting short scenes and songs, but when a sequence clicks above the three-minute mark you can feel the filmmakers flailing to maintain momentum. Sketches are a sprint, but movies are a marathon, and one The Lonely Island isn't ready for. "Popstar: Never Stop Never Stopping" feels less like a pulsing music mockumentary and more like a series of sketches slapped together. Though a mediocre movie, it's seriously funny, relishing in the sophomoric, occasionally shocking, and devoted silly.

"Popstar: Never Stop Never Stopping" opens June 3.