The bigest problem with books to movies in general is every one pictures characters diferantly while Harry Potter didn't have everything perfect like Ron & Lupin looked freackshly old fashon. I did like Suris for now though because he did look old but people with a lot of stress tend to look older than people the same age whith none & lets face it even a year in Azkaban could do that to a person! The actors are a bit to old but they can't film them all at 1 time because between movies a years soposed to pass.
Also it didn't mach the movie perfect they tended to move sence around & cancle others & put oter things to close (to do the book justise the movies really needed to be longer) but at leat it was close to the book some movies like Planet of the Apes, Dune, or Time Machine are complatly diferent than there book counter parts.
The 3rd movie did look better than the firts 2 but its not just because of the new director but because well lets face it the 3rd book kicks the other 2's butts just like I think the 4th & 5th ones have been getting progressivly better!
my bigest wory with the books is that the filmmakers will start pushing the writer to write them faster because they may make them faster than she can write them whish could make shorter & not as intersiting books.