Cool book. I recently read Dr. Jekyll & Mr. Hyde, which makes a nice companion piece to this since they're sortof about the same thing. Dorian Gray was published in 1890, Jekyll & Hyde in 1886; Wilde's apparently on record as admiring Jekyll & Hyde.
I think Wilde's lack of experience writing novels shows sometimes. James Vane is introduced so clumsily that it's instantly clear that Sibyl will come to an unfortunate end and James will take revenge. There's no other reason for his character to exist, right? "If he ever does you any wrong, I shall kill him." Not brilliantly subtle.
Jekyll & Hyde, by contrast, is a tidy little package by a master storyteller. But it doesn't reach for the same heights that Dorian Gray does. Wilde's not always successful, but I think he's set his sights higher.
I'm a little afraid that Wilde thinks Lord Henry is as charming as everyone in the book seems to. From quotes I've read, and from Wilde's preface to this book ("All art is quite useless"), Henry's paradoxical style seems to be an exaggerated version of Wilde's own. The problem is that Henry's a total bore. He's just constructing elaborate nonsense based on a formula. You could probably write a software program to deliver Henry-isms. "I'm tired!" "I tire only of sleeping." "That girl's hot!" "There's nothing so ugly as a pretty girl." Oh, shut up.