Those actors should! Many of them have appeared in big-name TV programs and feature films. You might not know their names, but maybe you've seen their faces. They are character actors.
Take Keith Szarabajka, who plays Arson Detective Herscel Biggs. The actor played Detective Stephens in The Dark Knight and appeared in Season 4 of 24.
Others include Garla Gallo, who played Gloria Bishop in L.A. Noire's "The Fallen Idol". She's appeared in The 40 Year-Old Virgin, Superbad and Bones. Actor Ned Vaughn plays L.A. Noire's traffic desk captain; recently, he's appeared on Mad Men. Courtney Gains, who's appeared in Back to the Future and Memphis Belle, plays a suspect in L.A. Noire's Golden Butterfly case.
Of course, L.A. Noire protagonist Cole Phelps is played by Aaron Staton of Mad Men. His performance, and the performance of the other actors, was captured with high tech cameras that filmed scenes from multiple angles.
Click through the link below to read more about L.A. Noire's character actors.