What a stunning piece of art! You have outdone yourself ones again, the shadings are very nice and the contrasts are great, which gives it much depth. The figures looks very lively, especially the eyes which are looking at one. The mood of the reference is well captured, very dynamic and you captured their outer appearance perfectly! What I also like are the textures and the details, especially on the Griffindor sword and on the clothes. What you could improve are the smaller details, the hair can easily identified as drawn, same goes for the dark areas where the pencil strokes can be seen very clearly. But you have improved a lot within the years, keep your work up
First, I must say that I like this drawing. The theme, though popular, is not generic - Especially this reference picture. Your technique is also very good. I like the use of dark shades contrasting the lighter ones, which adds to the vision. My favourite part is Harry's face which in my opinion is the best drawn - Especially the spectacles. Also, I like the details in the sword, and the lack of details in the background: It helps concentrating on the characters.
I think, however, that in some places you used too sticking out black lines: It can be mostly seen in Ron's collar, but also in some other parts. Also, Hermione's hand looks less realistic than the rest of the drawing, probably in part because of the dark contour.
Okay, I have seen many good Fan arts of Harry Potter, but this is really awesome! When I saw it I simply had to hunt down my chamber of secrets DVD and compare it. The similarity is stunning! I love how you put in all the details like the shadow of Harry's glasses while filling out the whole page, too. What I like most is Ron's facial expression...I love Hermione and Harry, but Ron always lights the mood...I mean, honestly, follow the butterfly's?! ;D