The first thing to do is ignore the advertising that makes Hollywoodland look like the latest in a long string of Los Angeles period mysteries. To be sure, it is a period piece, and a great one at that; and one of its two protagonists is a classically cynical gumshoe who's only interested in the money. But far from being a whodunnit - indeed the overarching question of "what happened?" doesn't even have an implied answer - this is a story about two men who got eaten up by two very different faces of Los Angeles, one of them dying for it and one finding inspiration in that man's wasted life to better his own.

But I get ahead of myself.

The film opens in the middle: the event that one man's story inexorably leads to, and the event that will launch another man's eventual quest for self-knowledge. On June 16, 1959, George Reeves, star of the television series Adventures of Superman was found in his bedroom with a bullet in his brain. A day or two later, a venal little detective named Louis Simo is put in contact with Reeves' mother, who refuses to believe that her son shot himself. So begins an investigation.

I said it's not much of a mystery, and I stand behind that, but I'm not sure that was the intent. On one hand, it really does seem that Simo is meant to follow in the tradition established by Jake Gittes. But the plot really doesn't bear that out much: we know what Simo learns, because we see the last decade of George Reeves' life played out in flashbacks, but we never really find out how he learns it - he does precious little detectiving for the first two thirds of the film, and he knows details that do not suggest his canny investigation so much as they imply that he is watching the film that he's starring in.

That quibble aside, Louis Simo has one important characteristic he shares with the heroes of virtually every masterpiece of detective cinema: he's a parasite and he knows it, and by and large he's not bothered by it. He makes his money stringing along paranoid spouses, he takes the Reeves case largely to get his face in the papers, and he ends up with an innocent death on his hands.

It's not immediately obvious even though the film is structured to take advantage of it, but Simo's story is essentially a parallel to Reeves': he starts as a struggling matinee player, carefully placing himself wherever the camera will find him, and in this way he stumbles across Toni Mannix, the wife of MGM's general manager. They strike up a passionate affair, with Toni glad to have a gigolo to combat her husband's string of mistresses, and Reeves ultimately lands the role of Superman, dooming his career to a life of typecasting with the very first decent job he's landed.

Both stories are ultimately about lives wasted: and it is only by witnessing the toll that it took on Reeves that Simo can pick himself out of the sordid gutter that he's been lying in for so long. The relationship between the two men is curious, a sort of homosocial twist on Laura, the detective becoming obsessed with a dead man. Throughout they are contrasted: Reeves is already a big man before the Superman suit, Simo is mocked for trying to puff up his scrawny frame to look like a tough guy; Reeves stops smoking (in flashback) shortly before the gum-chewing Simo scrabbles for his emergency cigarette; Reeves disdains children, while Simo, we ultimately find, is torn up above all else by his separation from his son.

It's difficult to think of Hollywoodland as anything other than a character study, not because it is deficient in other ways, but becasue the film is dominated, surprisingly, by Ben Affleck's performance as George Reeves. It was a brilliant casting choice, and far less intuitive than it seems: one rectangular actor of negligible ability playing another. Affleck's performance is nearly flawless: he totally embodies the frustration of a man who cannot help but watch how quickly life is passing by. This isn't the first wave in a full-fledged Affleck revival, but rather the moment an actor finds precisely the role he is perfect for.

In fact, it is almost a problem how fully Affleck realises his character, because it leaves the non-Affleck scenes empty by comparison. Adrien Brody is a fine performer, and he gives one of his better performances as Louis Simo, but it is unmistakably a performance, and it isn't anywhere as interesting as his co-lead's. His scenes are largely an exercise in waiting for Ben's next appearance. Diane Lane fares much better, as Toni Mannix; she naturally has the exact look of a fading '50s starlet, and here she couples that with a pragmatic recognition that she is aging, doubtlessly a familiar feeling for a woman whose made it her business to snap up all the good roles for women Of A Certain Age. Bob Hoskins rounds out the leading cast in the small role of Toni's husband, giving him little to do but appear gruff, something he cannot help but do well.

The film captures the look of the 1950's surpassingly well; the decade has been experiencing a bit of a cinematic revival lately, but not even the immaculate Good Night, and Good Luck. has such a lived-in feeling to it. Every set and every costume looks worn and tired, incidentally making this the best film in recent years to describe the exhaustion at the end of eight years of Eisenhowerian white-bread pageantry. Perhaps regrettably, the cinematography does not follow suit; unlike GN&GL or The Notorious Bettie Page, for example, this looks like a film shot in the 2000's. Competently-shot, mind you - especially some very fine late-game night scenes - but it does detract a bit from the otherwise flawless recreation (and I suppose that a truly '50s-style photographic language would have lessened the impact of color; Reeves moves from brightness to dim shades, which is where Simo spends the whole film).

Nor is that the only flaw. Besides that, and Brody's inability to keep up with Affleck, Hollywoodland is roughly the 300th consecutive film for which I must complain that it's too long, and as usual it's in the end: as Simo gets further into the mystery, it becomes more of the Chinatown-wannabe that it so delicately avoided in the beginning. And if the cinematography is merely workmanly, the editing is sloppy: in the worst cases it is impossible to tell where people are standing relative to each other, but throughout there are far too many places where a scene feel to end a beat before or after the point that it actually cuts to the next scene; and plenty of those scene transitions, especially when a flashback is involved, are distracting and confusing.

Small complaints. This is one of the best character-driven pieces of the year so far, and while it is perhaps dubious as a Reeves biopic or historical inquiry, its translation of reality into fiction leaves it one of the most clear-eyed depictions of losing oneself to one's work that recent cinema has produced. It is perhaps less than it wants to be; but what remains of it is remarkable.