My interest in Gosford Park flows from having read that the only "real" character in the movie is the famed musician, movie star, playwright, song composer and composer and sometimes librettist of hit musicals, and I hoped to get a full serving of Novello's music.
Well, long before I purchased the DVD I had come to realise that Novello's music and character would be but a small element in the movie. Nevertheless, I bought the DVD and have to say that I am not disappointed with it. It is a great period piece, with a great cast, and an interesting who-dunnit plot. But, it won't illuminate the life and times of Ivor Novello.
I have to say that I found the extras with the DVD most interesting in terms of how Altmann directs, how the story line came to be developed, and how the cast of "egos," accustomed to acting to a lens, happily went about playing to an imaginary audience sitting just beyond the edge of the set, just as though they were playing live in a theater--and of course they had great live theater chops anyway.
In short, if you like the British TV period pieces, such as "Upstairs Downstairs," or "Downtown Abbey," or "Foyle's War," to give a sense of genre, my bet is that you will also enjoy "Gosford Park."