"The Black Dahlia," Brian De Palma's attempt at film noir, can be summed up in one word: over. Or, more specifically, one word with a few different suffixes attached to the end.
Like "over-directed." De Palma is definitely an auteur, his style is instantly recognizable either from his love of deep focus shots, blood and gore or homage to classic films. And sometimes it works, like the classic scene in "Untouchables" with a bloody shoot out and a blatant homage to the groundbreaking Odessa Steps scene in "Battleship Potemkin."
In this case, though, his style just interferes with the film. Random first-person point of view scenes make no sense, a nod to Hitchcock's "Vertigo" seems completely pointless. His attempt to make a noir film is so blatantly obvious it makes for more of a parody of noir than anything else. Maybe he forgot that the original noir classics were never meant to be in any particular style – until the French watched them after WWII and named them noir. Here the auteur style of directing just gets in the way; then again maybe the film only has style going for it.
Like "over-acted." Not only does every actor in the film try too hard (note to Josh Hartnett, glaring constantly does not make you Humphrey Bogart) but they're all terribly miscast. Both Hartnett, as the hard-boiled detective Bucky Bleichert, and Scarlett Johansson, as one of Bucky's love interests, look too young for their roles. Hillary Swank couldn't slink like a femme fatale even if she wasn't saddled with two famous roles portraying very masculine women.
Like "over-violent." De Palma is known for blood but usually it makes a point — or at least has Al Pacino shouting loudly behind a large gun. In "Dahlia," there is not a single act of violence shown that wouldn't have been more powerful off screen. Especially when the murder is shown — a quick cut away before the murderer slices into the victim’s mouth would have been more powerful and elicited fewer groans from the audience.
Finally, like "over-long." If the confusing plot, myriad of names and lack of cohesive scripting don't bore you, the film’s two hours and one minute (and you'll notice that minute by the end) of completely ignoring the interesting murder case and focusing more on social commentary and Josh Hartnett's relationships may well put you into a deep coma.
A coma in which you might dream of a classic noir film with a femme fatale who enters down a curving stair case as the camera pans up her legs and the detective doesn't look like a baby faced kid and directors don't try for a feeling but actually capture it.