I think Michael Gambon is great in some scenes and way off in others. I wish they had made him read the books, cause I don't think he quite "gets" it, and there's only so much the director can do to get the perfect performance out of him if he doesn't fully understand Dumbledore's character. One scene that comes to mind is in GoF when Harry's name comes out of the goblet of fire, and he runs up to him and grabs his shoulders and shakes him and demands to know if he put his name in the cup. Dumbledore would never act that way, especially to Harry. But then there are other scenes where he does get the little quirks and humor and wisdom that make Dumbledore so great. I think he's best in PoA and HBP (which is good, cause he needed to be epic in that one!). I think Richard Harris was a good Dumbledore too; to me, he had the look and the twinkly blue eyes and all of that. But I think Michael Gambon portrays him with more strength, which was needed. Overall, I like them both... I think maybe a blend of the two would be the perfect Dumbledore in my eyes.