Seen the 1h30 pilot : in my opinion it's not bad, you have nice casting choices (Siegel, Parker, Stax and Sid) and some scenes are good. There are scenes screaming too much '50 cinematography with average CGI like Magic City but the jazzy / noir ambiance is okay. On the other hand some casting choices (Teague and that trying-too-hard femme fatale) are average at best and you sometimes have that weird feeling main plotlines are on heavy rails.
But, I'm a James Ellroy's work hardcore fan and I like the post WWII LA social-politics setup. Therefore I kinda liked it, tho granted it felt like poor man's Boardwalk Empire meet LA Confidential, in some way. What's gonna be interesting is seeing how Darabont would get freedom as a showrunner and how far he'd control artistic direction.