- there is no twinkle in his eye like described in the book.
Yes, a combination would be good. A bit more of the silver hair and a more sympathetic manner - he has to an approachable headmaster which is not usual whilst being as believably powerful as Voldemort.
At the same time he has to have the authority and enormous kindness to take on the oddest assortment of staff - Snape, Lupin, Moody, Hagrid etc. and still juggle the Ministry of Magic.
In other words, he has to be the complete opposite of Voldemort. Michael Gambon needs to soften up his portrayal or Dumbledore a good bit when it comes to dealing with those who rely on his protection.