First of all, size. It's simply amazing for me that someone can draw on such a size. The biggest I used was B3 and it was a challenge. Secondly, how well you draw him. Robert Downey Jr has very characteristic facial features, especially eyes. I like how you used pencils to darken his face. I don't like over-brighted portraits. And finally, the way you coloured his hood red. It cathes the eye and really suit the drawing. Congratulations, it's an amazing portrait.
Damn it, I am drawing this exact picture of him right now, cus I hadn't seen any drawings of it so far And you come around and do this spectacular job on it. Now mine will pale in comparison... But seriously, awesome job there buddy