One of the Reasons DH P1 was so good is
Michael Gambon is not in it. True story, this guy is one of the main reasons why the Harry Potter movies are such a big fail in comparison to the books. Gambon has ruined Dumbledore every step of the way, so not seeing his face in DHP1 was like a breath of fresh air.
Not saying he's the only reason the movies were a let down - cutting out loads of important information, backstory and subplots are just as important - but when u misscast one of the most important and beloved characters in the Harry Potter universe you can't really expect hardcore fans to appreciate that.
I know it's been said a million times, but Harris did an astronomically better portrayal, even though he was older and fragile.