Six-time Oscar nominee Jim Sheridan, fresh off the success of his spellbinding family tale “In America,” looked at the life of multi-platinum rap star Curtis “50 Cent” Jackson and saw the makings of a great movie. Using bits and pieces of the man’s own – almost mythological – life story; his drug-dealing mother’s untimely death, not knowing who is father is, growing up selling drugs and enforcing street justice, being shot nine times and left for dead; he and “The Sopranos” staff writer Terrence Winter crafted “Get Rich or Die Tryin’” in which for the musician to star. The result should have something to savor, a work as gritty and superb as what Curtis Hanson accomplished for Eminem with “8 Mile;” a feature pulsating with the grime of the urban hoods and the beat of the music that saved Fifty’s life.

Should have, but isn’t, this glum and uninspiring melodrama one of the Fall’s most depressing disappointments. Winter’s screenplay is anemic, throwing clichés at the screen as if they were Shakespearean soliloquies ready for their debut at the Globe Theater. The film is a completely disheveled mess, limping from scene to scene with all the urgency of a snail taking his morning constitutional. At the center of it all is Jackson, mumbling incoherently through a lackadaisically unsubtle performance it’s nearly impossible to understand how he became so gosh darn popular in the first place (becoming the first musician since The Beatles to have four top ten hits on Billboard’s Hot 100 at the same time).

Fifty plays Marcus, a thug and a drug dealer trying to right the wrongs he’s done in his life through music. But even after the birth of a child, the love of his childhood sweetheart Charlene (Joy Bryant) and surviving a brutal hit by a drug lord (who may be the man’s biological father), Marcus finds the call of the street difficult to resist. Yet resist he does, focusing his manic energies on writing in order to escape a life that can only lead to heartbreak, prison or, worst of all, death.

What’s most bizarre about “Get Rich or Die Tryin’” is how little, if at all, the movie focuses upon music. Music is what saves Marcus’ life. It is what gets him the love of Charlene, helps him survive in prison, gives him a focus for his rage and earns him the eternal friendship of fellow ex-con (and future manager) Bama (Terrence Howard). Music is why Marcus exists at all and yet music; its creation, its rhythms, its ethereal drive to make a person better than what they are; hardly has a presence in this feature’s worldview. Sure, Sheridan shows scenes of Marcus writing and singing from time to time, but these moments all feel like afterthoughts, brief reminders that, other than being a drug-dealing enforcer with a gun, his protagonist also just happens to sing.

It’s just all so blasé. I’ve seen this movie before, many times, and from “Dead Presidents” to “New Jack City” to even this summer’s wondrous sensation “Crash” I’ve seen it better. Best of all is another movie combining urban street life with music, Sundance phenomenon “Hustle & Flow” (which, as it happens, also stars superstar-in-the-making Howard). That late-August independent stunner just looks better and better the deeper we get into the year, brilliantly making an audience care for an amoral monster as he and the people around him are slowly redeemed by the powerful thrust of poetical music. Every beat, every movement of that movie felt alive, lived-in, as if we as viewers were right there going through the muck and grime desperately reaching for something – anything – just a little bit better with him.

Sheridan, Winter and Jackson never come close to achieving anything like that. As good as the film looks, frequent Sheridan collaborators cinematographer Declan Quinn and production designer Mark Geraghty do exemplary work, the whole thing falls so curiously flat the result is almost absurdly mystifying. Great actors like Howard (who is the most dynamic presence in the entire picture), Bryant, Viola Davis and Bill Duke are left high and dry, so underdeveloped and out-of-place you get the feeling they all probably wonder why it was they signed up for this mess in the first place. Only Adewale Akinnuoye-Agbaje of HBO’s “Oz” truly rises above the material, adding menace, charm and mystery to a movie curiously devoid of all of the above.

The most perplexing question, though, is what it was that drew Sheridan to the story in the first place. He’s talked at length in interviews and in the feature’s production notes about how much Jackson’s story resonated with him, how the parallels to his urban life compared so completely with the Irish stories the filmmaker has been telling with unabashed passion in nearly every single one of his cinematic forays. If that is true, none of those parallels made it up onto the screen, all of them so stunningly absent it’s almost as if the director purposely decided to leave them out.

This, of course, makes absolutely no sense, especially if you consider Sheridan’s heretofore stunningly strong track record of success. But happen it does, and watching “Get Rich or Die Tryin’” fall so squarely upon its face is like watching Martha Stewart bake an Upside-Down Cake right side up. It just isn’t any good, and no matter which way a person wants to spin the record, that’s the kind of rock-solid truth even Hercules himself couldn’t break apart. In fact, even for Fifty’s fans, the best thing anyone can do with this particular piece of music is turn the damned thing off.