I'll start off with something positive for once:
Mia Kirshner (yay! 24!) is worth every penny as the ill-fated Elizabeth Short. She is innocent and childlike. Calculating and cold. Deep when the words seem incredibly shallow. The 10 mins of screen-time definitely provided relief when Josh Hartnett's unrelenting brooding and Brian De Palma's stylistic shots proved gag-worthy. It's not enough to LOOK film noir guys...
I found it pretty funny that for something named "The Black Dahlia" it had little to do with that case and more with Josh Hartnett's insecurities and inability to connect two-two together. If these fictional cops were anything like the real-life detectives burdened with this case, it's no wonder it has yet to be solved.