Well it was a different actor AND a different Director.
The guy who played dumbledore in the other two movies died before or during the making of the last one so they had to bring in someone else.
And although the director of the first two was a producer for the third...he was not the director...which also explains why there are so many differences in the third (from what I have read) compared to the other two....even the school grounds are different in the last one.
One other problem is that the first two books were not very big so they could stick to the books closer in the long movies....the last few books are HUGE compared to the first two so many things will be sacrificed.
I am still looking forward to the DVD.
Funny thing is I would have had nothing to do with Harry Potter if it were not for my wifes 9 year old sister...who insisted we get the DVD because her friends liked it and she wanted to watch it....after watchng the first two movies I liked them.
Then she brings a list home from school...it is a book list and the books on that list have credit points given to the student if they read those books (extra credit points in a reading program).
So we buy the first 4 books in a box set for her...she read ten pages and has not bothered with it since then....I went and bought and extra set for the wife and I...and then got the Order of the Ph book.
I have read them all 3-4 times and am reading the last again now.
I will say that those that think these books are for most 9-10 year olds just do not know about them.
These really are for older kids and adults...I think many adults really enjoy them.
She really is a good author and it has surprised me how good the books are and the ability she has to string clues along the series and keep one interested...her books really flow and when waiting for the next book it still holds your attention and really anxious for the next one to come out.
BTW...they are currently filming the Goblet of Fire and she is halfway through the 6th book...titled Harry Potter and the Half Blood Prince (for the record she says that Harry and Voldemort are NOT the half Blood Prince).
For more info on Harry...for those bored and who like the books....try these links.
http://www.mugglenet.com/
http://www.hp-lexicon.org/
http://www.jkrowling.com/
The last one is the authors site...I suggest using the text only version of the site as the gui/flash one is crappy.