Such a nice renderation of the HP poster.. its not anime art but definitely deserves more attention! ^_^~ It looks like a perfect cover illustration for the HP book series.
Watercolours are a hard medium to control and it can make or break great artwork. In this case, you used it to your advantage. The color scheme is true to the original, though I would have liked to see his head tilted down a little for dramatic and cool effect like in the poster.
But great work though.. keep drawing like this, lucifer-michael. ^__^ I'd love to see Hermione and Ron next time!