Personally I think the background has been a bit hit and miss this edition, with the 'Grimdark' ebbing and waning at different points. Not a fan of the new Slaanesh look, which looks to have gone backward in design. and a few other things seem silly.
BRB : The darkness was definitely there. C:SM : Missing something C:IG : Definitely has it. C:SW : Wolfy Wolf Wulfen spoils it. C: Nids : Has it. C: BA : Something is again not right. C: Crons : Has it. C: GK : Spoils it by being OTT. C: DE has it in good amounts.
Saying that, Black Library is good as ever and Forge World has some good stuff in their campaigns.
Is it just me getting older, or was the older stuff really as gleefully dark as I remember it, and what's your take?