Good vs. Evil is a prominent theme. Dorian is an innocent, pure soul before Henry meets and influences him. Basil, Dorian's true friend and artist, did not want Henry to meet Dorian to meet Henry for the very reason that Basil knows that Henry enjoys toying with people as a life-long psychology experiment.
Because of Henry's influence and his philosophies on Beauty, Indulgence, Art, and life in general, Dorian makes a deal with the Devil and only the picture shows the extent of his sinful behaviors while his physical appearance remains untarnished and beautiful.
Beauty, Art, and Indulgence are three other good themes, as well as the supernatural aspect of dealing with the Devil and remaining young forever because of the deal.
The indulgence of the senses is one the the main themes in this novel. Lord Henry believes that one should not deny oneself of their impulses and desires, and Dorian attempts to follow this view.
In order to live life well, the senses must be indulged. Intellectual matters and education are less important that art and beauty in this novel.Dorian's interpretation of Lord Henry's advice leads to suicide, murder, and the destruction of human lives.
Whether Dorian misinterpreted Lord Henry's views, or the views of Lord Henry's Hedonism themselves are flawed, is up to the reader to decide.