Alan Rickman was amazing but I’d love to see age-accurate actors for Snape, Lupin, Sirius. In the books they are supposed to be in their 30s throughout. Harry’s parents are supposed to only be 21 in the flashbacks as well. Yet they used considerably older actors for all of them.
I really hope without the constraint of fitting it all into 8 films they are able to be as true to the books as possible.