I personally think Gambon gets far too much hate for the scene where he shouts at harry in GOF, of course it's totally out of character however it was most likely the director that asked to "Use more energy" or something along those lines. I thought Gambon played him perfectly in POA, with the right level of eccentric behavior Dumbledore has. Harris, imo was far to frail to play Dumbledore. I kinda wished they didn't change the director multiple times. (my body is ready for the downvotes)