Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Alternately Admiring and Judgmental
Admiring and judgmental? We know this sounds complicated, but stick with us.
We get the distinct feeling that the narrator here is torn between fascination and disgust—Lord Henry and Dorian's depraved philosophy is both appealing and revolting at the same time. This narrator is certainly interested in the beliefs espoused by the decadent characters here—the descriptions of Lord Henry's brilliant wit and rhetorical skill (see Chapter 3) express a complete admiration and fascination with this character.
The descriptions of Dorian's incredible physical beauty are also invested with the same kind of near-obsessive, swooning admiration:
Yes, he was certainly wonderfully handsome, with his finely curved scarlet lips, his frank blue eyes, his crisp gold hair. There was something in his face that made one trust him at once. All the candour of youth was there, as well as all youth's passionate purity. One felt that he had kept himself unspotted from the world. No wonder Basil Hallward worshipped him. (2.2)
However, because this was a book intended for publication and sale, the narrator has to come down pretty harshly on these immoral characters—the tone grows increasingly judgmental and critical towards the end of the novel. We start to see that Lord Henry is a truly warped and flawed being, and that Dorian himself grows less and less compelling as he gets more paranoid (after all, desperation is not sexy):
He was prisoned in thought. Memory, like a horrible malady, was eating his soul away. From time to time he seemed to see the eyes of Basil Hallward looking at him. Yet he felt he could not stay. The presence of Adrian Singleton troubled him. He wanted to be where no one would know who he was. He wanted to escape from himself. (16.16)
The tone of the narration is also extremely judgmental throughout with regards to characters who aren't worthy of praise—ones that are either too stupid or too uncultured to merit Wilde's interest, or are just women (for example, Mrs. Vane and Lord Henry's wife, Victoria).