Grade: C-

Who could have thought that Johnny Depp would ever play a part that once might have gone to Barbara Stanwyck or Joan Crawford? But that’s what happens to him in the last thirty minutes or so of the biographical drug drama “Blow,” which tells the rags-to-riches-to-rags story of George Jung, a callow, shiftless American who joined forces with Pablo Escobar to fashion a huge U.S. market for cocaine during the 1970s. After a stint in prison, an impecunious Jung grieved over the loss of his family and desperately tried to build a relationship with his adolescent daughter Kristina. This is the episode treated during the latter portion of “Blow,” and the ostentatious suffering George goes through pining for his kid would have suited Mildred Pierce. There’s one major difference, though: a Hollywood grande dame of the forties would have had a much better hairdo. Depp sports a shaggy hippie mop so scraggly and unkempt that one suspects birds might take up residence in it.

Otherwise, “Blow” proves a surprisingly flat and pedestrian treatment of a potentially intriguing story. As constructed for the screen by scripters David McKenna and Nick Cassavetes and directed by Ted Demme, it’s a standard-issue cautionary tale about how drugs destroyed the promise of a bright, energetic young man who might have been successful and respected had he applied his talents to some other field. We watch Jung as he leaves his midwestern parents, understanding failure Pop (Ray Liotta) and shrewish alcoholic Mom (Rachel Griffiths), for the good life in California; gets into small-scale drug-dealing with flamboyant supplier Derek Foreal (Paul Reubens); enjoys a brief, doomed romance with Barbara (Franka Potente), who shortly expires; links up with a Colombian connection when he serves a jail term with Diego Delgado (Jordi Molla); becomes a major player and marries Colombian gal Mirtha (Penelope Cruz); loses his role in the operation to Diego; gets arrested and sent to prison again; loses his wife and daughter Kristina (Emma Roberts) as a result; and gets out, only to stumble disastrously into the drug trade one last time in a vain attempt to win back his kid. The tragedy of this wasted life might have been depicted with some power, but the treatment given it in “Blow” is peculiarly lightweight and unaffecting. It’s all so conventional and unimaginative that despite its big budget, it resembles the sort of pallid TV movie that might screen on an off night on HBO.

The acting isn’t particularly good, either. Depp might have done a lot of research to capture the real Jung’s mannerisms and personality, but even so George comes across as a rather dull, passive guy. Depp ages particularly badly; in the later scenes he’s encased in poor makeup, and his gestures aren’t remotely convincing (that awful hair doesn’t help, either). Liotta grows old much more persuasively, and he gives a nicely modulated performance very different from his manic turn in the current “Heartbreakers.” Cruz is billed over him, but she’s much less memorable; for most of the running-time she’s just a standard-issue stereotypical Latin spitfire, though she calms down a bit in the final reels. Griffiths, a much better actress, is poorly cast and shrill; she’s far too young to be convincing as Depp’s mother, and her heavy theatrics go against the narrative’s looser rhythms. Potente makes very little impression at all (though she looks a lot taller than she was in “Run Lola Run,” or maybe it’s just the result of playing against Depp), but Reubens has fun with his over-the-top character. Molla is generally decent as Jung’s traitorous partner, but in his last scene he appears to be doing a very poor imitation of Al Pacino’s overwrought turn in “Scarface.” The always amusing Max Perlich makes a brief appearance as one of Jung’s cronies, and lumbering Ethan Suplee disappears from the action all too quickly as his California roommate Tuna. Bobcat Goldthwait does a cameo; he hasn’t grown any subtler over the years.

Ted Demme’s direction can be praised for not overdoing the 1970s-80s atmosphere, and he occasionally employs techniques characteristic of pictures of that era, something that film buffs will get some enjoyment out of noticing. But his helming is mostly flaccid; the individual episodes drag more often than not (an exception is Jung’s meeting with Cliff Curtis’ genuinely scary Escobar), and they’re not very smoothly linked. As a result the picture lurches forward from moment to moment, and the culminating sequences of reverie and regret, far from ending the picture on a high note, are among its least successful.

“Blow” obviously has the right intentions, and its makers seem to have been genuinely committed to producing a useful commentary on what the drug trade does to its practitioners as well as their customers. But when compared with a film like “Traffic,” which treats of a similar subject with far greater cinematic skill and emotional power, it’s distinctly third-rate.