The actor told the Reader's Digest September issue that he was not a fan of last year's episodes.
"We're remembering that there was a world before the First World War," Cumberbatch said of his role in BBC Two's Parade's End.
"We're living in a culture now that's revering, or having a nostalgia trip with, the beginning of the 1900s.
"Although Downton traded a lot on the sentiment in the last series... but we won't talk about that series because it was, in my opinion, f**king atrocious."
He added: "There was that fear, yes. I thought, 'Are we pandering to a taste?' But this is so much more sophisticated, so much more unusual.
"You rarely see a piece about this class of people that's this accurate, funny and pointed. We're not making some clichéd comment, 'Oh, isn't it awful the way there's this upstairs-downstairs divide'.
"This is about class and love, an elegy to a dying era. It's the final mad waltz of Edwardian society into this war-game idiocy."
Cumberbatch said of the era: "Everyone was held in their place, but what was honourable about it was that there was a duty of care from the top down.
"That shouldn't be tied in with any sort of fat-faced, flatulent Cameron effort at what Toryism - horribly - is now."
Reader's Digest is out next Tuesday, August 21.
Watch a trailer for Parade's End below: