Other films like this?
The film that comes to mind that is most like this, besides Atonement, is The Shooting Party. Although sex and love are not at the center of that movie, it is set maybe five years after this one, and the theme and atmosphere are similar. Also, The Shooting Party stars James Mason. Amazingly, I'd never heard of The Go-Between. Are there other sleepers out there I may have missed?
I've already mentioned Far From the Madding Crowd in another post.
BTW, I was amused at one of the IMDB user reviews that referred to the setting as "one of the most historic estates in England." There are in fact grand houses like this all over England. This particular house, I read, was derelict before it was taken over and remodeled for this film.