TL;DR - a true blue masterpiece, and one that is going to make me start a classics binge shortly.
Whether it is the characterisation, the heady Faustian themes, and a surprisingly great plot - my first foray into Wilde's literature was nothing short of spectacular. Lord Henry's cynicism was laugh-at-loud at parts, and somewhat deep at others, but where the novel truly shines is in depicting Dorian's corruption - first as a charming and uncorrupted seventeen-year old, but then whose countenance grows darker the more he revels in his senses. What I liked the most in this depiction is that we get to know about Dorian's behaviour second-hand, and that too in parts - thus the misuse of the omniscient PoV is kept to a minimum.
A slight addendum - there are slight socialist undertones I got from this (for example, the depiction of vacuousness of the people having inherited wealth is unsubtle), to the point where I began to wonder if Wilde was a socialist - which he was? Unsurprising, but it only added to my appreciation of the text.