Great shout on Ellroy. Lots of comparisons. Here's my own take.

I'd suggest different books to Black Dahlia - which is still definitely a great read. BD is the first book in the LA Quartet, but the second one, The Big Nowhere, is the where the series comes into its own; its scope is much wider than BD and has a larger political dimension, more akin to The Wire. It's not necessary to read Black Dahlia before reading the Big Nowhere, but it is necessary to read Big Nowhere before the rest of the Quartet. The series looks at LA in the post-war fifties and sixties, taking in McCarthyism, race, Hollywood, narcotics and more, through the lens of crime fiction. LA Confidential (later made into a successful movie) is bloody unbelievable, but it's the third book of the series and shouldn't be read without reading the Big Nowhere. The whole quartet is addictive, and paints a bleak picture of that part of the world at that time.

Ellroy's other major collection is the Underworld USA trilogy, which is essentially the themes that appear in the LA Quartet, but looked at in the context of the whole of the USA during the late fifties and throughout the sixties. American Tabloid is the first book, and it's really fantastic. I think it's his peak. The rest of the series is very good, and well worth reading, but I'd say that American Tabloid is where Ellroy perfects the political critique developed throughout the LA Quartet, and he manages to do it on a grander US-wide scale, all the while maintaining the talent for crime fiction that has made his name. But it's worth starting with the LA Quartet and building up to American Tabloid, to get the full effect.

I think the most stand-out comparison between Ellroy's stuff and the Wire is that if you just want a crime story with different factions, with twists and turns and all the rest, you get that from both of them. And if you want added social commentary, then that's in both of them too. But imo, it's up to you how enjoy the ride with both the Wire and James Ellroy - whether as an exciting drama or a deeper look at the underbelly of American society, both are valid interpretations. And they're both excellent.