What starts as a potboiler mystery about tragedy in Tinseltown barely manages a tepid simmer by the end in Hollywoodland, a film carried only so far by good acting and immaculate period details.

If it feels like a so-so HBO movie that made it to the multiplex, it’s no accident. Director Allen Coulter cut his teeth on such beloved HBO series as Sex and the City and The Sopranos. Writer Paul Bernbaum’s TV credits carry a smaller, and less confident, cachet, having moved out of Halloweentown and relocating to Hollywoodland

Most might not know the film’s title is the full word that the Hollywood sign used to spell out, reflecting its inability to offer entry points as seductive as those in Chinatown or L.A. Confidential. Instead, Hollywoodland’s story is unsure where to put its focus, with little of interest for anyone who’s not a California native, obsessive Superman fan or hardcore aficionado of actor George Reeves.

Hollywoodland has been hailed as a triumphant return for Ben Affleck — slowly but surely battling his way back from any number of terrible movies — playing Reeves, whose 1959 death by gunshot ended a body of work that was defined for better or worse by his role as Superman on ’50s TV show The Adventures of Superman. Affleck doesn’t have a revelation in rediscovering his talent, but gets the best role he’s had in a long time — showing off the nice nuance you remember he’s capable of as a man typecast all his life onscreen and off.

Reeves’ death is ruled suicide by the coroner, but his mother (Lois Smith) suspects foul play and enlists two-bit gumshoe Louis Simo (Adrien Brody) to rattle the cage for the papers and the police.

An absentee father living out of a fleabag motel, Simo puts off his own home-life problems for an investigation of: Reeves’ money-grubbing fiancée, Leonore Lemmon (the naughtily electrifying Robin Tunney); his sugar momma Toni Mannix (the fiendishly sexy Diane Lane), who bought Reeves a house where she could cheat on MGM studio-boss husband Eddie Mannix (Bob Hoskins); and Eddie Mannix’s bulldog PR man, Howard Strickling (Joe Spano), who might be more muscle than media.

Of course, Reeves might have just shot himself, but his relationship with each person is detailed in flashbacks that work as a story about Reeves, but not in connecting him to sad-sack Simo. Brody does a fine job early, but his role feels badly beefed up after the Oscar-winning actor showed some interest in taking it. Making Simo’s resolution of the case a good-karma quest reduces him to a blubbering boob in the third act, riding around in a Jack-and-nicotine haze with a busted face.

It’s much easier to marvel at sumptuous recreations of 1950s settings and fashions by production designer Leslie McDonald and costume designer Julie Weiss, both doing Oscar-level work. Hollywoodland tries to rumble all those authentic cars down a boulevard of broken dreams for all of its characters, but might have been better showing the sadly stalled-out journey of Reeves.