I'm looking more from a lore perspective than a mechanics one. D&D isn't a generic RPG like GURPS and I'm fine with the normal PHB rules being overlayed with a pulp or horror or sword and sandals theme. I don't need D&D twisting and removing rules and options to make it fit a genre (or the first printing of the setting from a decade or more ago).
What I am talking about is there is only a whiff of actual people, places and such to interact with. It takes the mile-wide, inch deep approach and misses a lot of interesting things to do with each setting. Eberron is a great example by boiling down Khorvaire's Five nations into sketches that barely give enough useful info for running an adventure in them. It's almost required you find a wiki or older book to know more. I guess it's to "make Eberron your own" but it makes running anything not in Sharn a diy project.
And Xen'drik? The jewel of 3e Eberron and setting for the MMO? Barely anything on it.
I mean I'm thankful I have a Eberron and Ravenloft book at all, but I guess I miss the more through takes of the ECS or DoD...