"Get Rich or Die Tryin'" tells a variation on the story of 50 Cent's rise from the grit, guns and drugs of the mean streets to the relative comfort of the rap recording studio. It's a tough transition for the hero and for the movie, which loses most of its dramatic clarity once 50 (or "Fiddy," if you want to get hip about it) gets out of jail and starts paving his way to stardom.

Technically, "Get Rich" isn't the 50 Cent story, even though it stars the superstar rapper, borrows liberally from his autobiography "From Pieces to Weight," and goes by the same name as his major label debut. The movie uses neither his stage handle nor his given name (Curtis Jackson). Instead, he's called Marcus (a.k.a. Young Caesar), much as "8 Mile" rechristened Marshall "Eminem" Mathers as Jimmy "B-Rabbit" Smith. "Get Rich" is a tougher, bloodier version of "8 Mile" that never quite matches that earlier film's depiction of rap as a means of self-expression and legal upward mobility.

Which isn't to say "Get Rich" is poor. Director Jim Sheridan, best known for his collaborations with Daniel Day-Lewis ("My Left Foot," "In the Name of the Father," "The Boxer"), turns Marcus' hardscrabble South Queens existence into a dark, never-ending war over cash, power and respect. Currently at work on a film about Irish crime in Hell's Kitchen, Sheridan understands the sudden, spasmodic nature of turf battles. "Get Rich" plays like a genre movie with a particularly skilled hand at the helm.

Marcus grows up under squalid circumstances, with a mom (Serena Reeder) who slings cocaine for a living and a dark, crowded house where he practices his rhymes late at night. When Marcus' mom is slain early in the film (a moment strangely devoid of emotional heft), the kid's response is chillingly matter-of-fact: "It was time to join the family business." Establishing himself as a worker bee in the local drug trade, overseen by the hulking Bill Duke (who has an uncanny ability to blend softness and menace), Marcus makes moves that he hopes will lead to a life of luxury.

"Get Rich" is peopled by the kinds of gangstas and hoods you can find in the songs of the late Biggie Smalls, or, of course, 50 Cent. (One pivotal scene, which plays twice from different perspectives, could almost be narrated by Biggie's "Gimme the Loot.") Screenwriter Terrence Winter, who has distinguished himself with his work on "The Sopranos," manages to juggle multiple characters and grievances between the likes of the lethally ambitious Majestic (the London-born Adewale Akinnuoye-Agbaje), the hair-trigger Bama (Terrence Howard, continuing a string of remarkable performances highlighted by "Hustle & Flow") and the foot soldier Justice (Tory Kittles).

Marcus eventually ends up behind bars, and when he gets out, the movie seems to lose its focus and will. It's hard to know what's important and where we're going as Marcus makes gestures toward settling old scores, fathers a child with his comparatively proper and underwritten girlfriend (Joy Bryant), recovers from a botched murder attempt and navigates the often slender line between the crime and rap scenes. The narrative gets sludgy, and the denouement comes and goes in a "That's all?" flash.

For all the richness in "Get Rich," the rap angle gets a little lost in the mix, even if the soundtrack has street cred to burn. You never feel the "8 Mile" or "Hustle & Flow" rush of a thug transforming his pain into art. The metamorphosis is muted into the background of a busy if vivid tapestry. In the end, you're left feeling as if the 50 Cent mythology could belong to almost any tough, ambitious survivor with a body full of bullets and a need to grab the mic.