I have to say that I really haven't cared for any of the movies. I've been disappointed everytime I go. I can't make up my mind if it's bad screenwriting or bad directing or just the movie "image machine". I know the actors are much better than they are in these series of movies, I've seen them do better in other things.
Liam Aiken was "Klaus" in the Series of Unfortunate Events movie. He actually did a very good job as a tragic waif. Also his appearance, except for the hair, seems much closer to the book discription of Harry. Skrawny skinny, messy hair, scruffy appearance... just more like a real kid than a movie set, wholesome waif that Dan seems to be.
Another kid who might would have made a good Harry was the kid in Peter Pan, he looked like he'd have been a right little hellion.