The basic premise is that, in London of roughly 1895, Emma, a housemaid, falls in love with William Jones, the heir to a merchant family that was elevated into the gentry sometime in his father's lifetime. What I love most about it is, it never once shocks you out of the time period. It's a truly adult romance story, which I love.
So Emma's meek and demure and all those good things, while William is a bit of a space cadet. While he can be entirely charming when he wants to be, he really doesn't realise that being charming to a shy debutante will make her fall in love with him. He announces that he's in love with a maid to his entire family and tells his father, "I'm sure society will understand in time" and, well, I'm sure the fangirls agree, but his father and I (and Emma) can't help but think the boy's a bit clueless.
I guess I like it so much because the author seems to be sending the message that it takes more than attraction to make things work. When someone finally yells at William for being a total ass to the debutante, Eleanor, and he finally treats her right, I cheer even though it means he can't be with Emma, because what he and Emma realise at the end of the first season is that they wouldn't have been happy together, not really--beyond affection, most of the people they knew would have made their lives a living hell.
It's possible the story will come up for a way for it to work, but it will be because they will find specific ways to remove all those obstacles (there's always the beloved Victorian trick of making Emma the orphan of some rich nobles, I don't know) but there's also the fact that it will hurt, but if William marries Eleanor and Emma gives the time of day to the hunky footman at her new job, they could all actually be happy and perhaps look back on the doomed romance as something that made them both open up, to other people if it wasn't possible to be together.
And that's so much more satisfying.