It's a tough one, because in the Preface he explicitly says that there is no such thing as a 'moral or an 'immoral' book, only good and bad books. However, I would say that there is quite an explicit moral in the story - Dorian Gray does end up getting punished for his egotism, vanity, unhealthy obsession with youthfulness, and his decadence and profligacy. Basically the society that Dorian and Lord Henry live in is revealed as an empty sham - even when Dorian does a 'good act', the portrait still gets worse because he only did something good out of hypocrisy and for the novelty of it. So yeah, there is a definite sense that no matter how good you are at covering up your sins and appearing 'good' to the outside world, in the end your soul (represented in the novel by the painting) will become rotten through and through and bear the consequences of your actions.