Given Martin Scorsese's almost unparalleled passion for movies, it's not exactly surprising that the best parts of his problematic new biopic of Howard Hughes, "The Aviator," focus on the eccentric tycoon's days as a filmmaker.

Hughes, we learn, was obsessive about the details of his films and willing to spend any amount of money to fulfill his vision, whether it was capturing the intense speed of flight in the World War I epic "Hell's Angels" or the specially engineered uplift of Jane Russell's breasts in "The Outlaw."

You can feel the palpable delight Scorsese takes in telling these stories and taking us to old Hollywood tribal gatherings at the Cocoanut Grove and savoring little details like when Hughes stops production of "Hell's Angels" until the weather cooperates and provides the kind of clouds he wants, clouds "shaped like magnificent breasts."

The man did have his fixations -- women, planes, movies. But as we also know, Hughes had his demons, too, and "The Aviator" spends a fair amount of time focusing on the Texan's fear of germs, his deafness and overall general nuttiness. And, frankly, the movie never quite makes us give a damn, a fault that can be laid on squarely on the expediency with which the film dispatches its psychoanalysis of Hughes.

In a way, this brevity is understandable. You don't necessarily want to be like Taylor Hackford's "Ray" and keep coming back to a childhood trauma and make it the be-all, end-all cause of every unpleasant episode in the man's life. (In the case of Ray Charles, it wasn't, by the way.) But neither do you want to open your movie as "The Aviator" does with Hughes' mother giving him an overly attentive bath and simply leave it at that. One bad scrub-down explains a life of obsessive-compulsive behavior?

Maybe there is no clear-cut explanation for Hughes' phobias. But if screenwriter John Logan and Scorsese are going to give us a crazy man who doesn't cut his toenails and urinates in milk bottles and expect us to empathize with the guy, they need to give us more to work with. But then, dramatizing Hughes' enthusiasms is easy, particularly for a man of passion like Scorsese. Finding the tension in a guy being afraid to touch a doorknob - that's a problem, and the solution eludes the filmmakers.

What you're left with are a lot of exhilarating moments, particularly whenever Hughes (played with consummate, engaging professionalism by Leonardo DiCaprio, almost compensating for the fact that he's not quite right for the part) is shown in the air flying one of his many newfangled machines. In these sequences, Scorsese marvelously blends digital effects with live action, creating some positively giddy (and terrifying, in a couple of cases) scenes of flight that are a joy to behold.

These moments compensate for the fact that, as a character study, "The Aviator" isn't exactly all that compelling or insightful. Logan's screenplay zeros in on a 20-year period, from "Hell's Angels" to his postwar business battles with Pan Am CEO Juan Trippe (Alec Baldwin, effective, if typecast, playing the heavy). There are romances with Hollywood royalty Katharine Hepburn (Cate Blanchett) and Ava Gardner (Kate Beckinsale), glimpses of Hughes' business genius, airplane test flights and a crowd-pleasing, get-off-the-mat finale pitting the film's hero against a sanctimonious U.S. senator (well-played by Alan Alda).

It's all superbly photographed by the incomparable cinematographer Robert Richardson and set in period worlds that are lovingly and immaculately assembled by longtime Scorsese collaborator Dante Ferretti. In short, it's a fine, handsome work, sporadically involving, but lacking (pervasively, persuasively, at least) the director's authoritative stamp. Ultimately, Hughes remains something of a mystery, as does the reason Scorsese was so interested in making "The Aviator."

TITLE: "The Aviator"DIRECTOR: Martin ScorseseCAST: Leonardo DiCaprio, Cate Blanchett, Alec Baldwin, Alan AldaRATED: PG-13 (sexual content, nudity, language, thematic elements, a crash sequence)GRADE: * * * (on a scale of 5)