Fangoria has some cast and filmmaker comments on the DG film, with some interesting things to note. Ben Barnes says, regarding Rebecca Hall's character:

[Dorian] doesn’t exploit Emily. Despite Henry’s fears, Dorian shows his humanity instead, making it a triangular, stake-raising moral dilemma.

So it seems Emily Wotton might be a replacement/equivalent for the character of Hetty Morton, the girl Dorian toys with for a while near the end of the novel, and then leaves, convincing himself that he's doing a noble thing.

Then Colin Firth says:

My character, Lord Henry, actually has an arc to play, whereas the book contains no journey or conflict.

Hmm. Surely Lord Henry's tragedy is that he doesn't develop? He only "spouts famous Wilde lines", fails to practice what he preaches, and learns nothing from Dorian's descent into sin. Lord Henry cuts a tragic figure in that regard, and in fact this aspect to his character is, I feel, one of the only things Will Self got right in this dreadful Dorian: An Imitation -- Lord Henry learns nothing, gains nothing, and all his wit is ultimately proven empty. I certainly hope he isn't made to suffer regret or redemption in the film. He is the devil, after all, or a certain kind of tempter, and that shouldn't be forgotten.