The poster effectively melds the man and the monster. The ruined side of Dorian's face is supposed to imitate the flaking canvas of the ruined portrait that bears the brunt of his decadence in startling contrast to his eternal youth.
But as one user at EmpireOnline pointed out, the effect can be somewhat hokey--"Finally...a film about eczema!!! " Offering my own critique, I would have liked for them to do something more with his hair.
It seems odd that the canvas effect would be limited only to his face, and a shock of white could have gone a long way to balance the effect. That is not to say I would want something a la Harvey Two Face, and perhaps that's something the designers of this poster were seeking to avoid.