I like the costumes and scenery. Not really getting into the storylines though, they are just too far fetched, to get myself involved with.
My Grandma, not posh by Downton Abbey standards (not had any maids in last 70 years of her life), but used to have two girls helping in the house (she doesn't use the term servant or house maid), when growing up. They never lived in, but helped her and her mum with all the chores (it was a six bed house, and in those days, there were no washing machines, freezers, and helpers were much more affordable). Similarly her father had employees in his business.
My gran tells me that she was always nice to the girls (good manners cost nothing), but never had any real dealings with them, or knew what was happening in their private life. She says that this mixing between the gentry and their workers, just never happened.