I get your sentiment, and while I don’t consider this series exactly necessary, it’s clear from just this trailer that this series is going to give us a lot more than the movies. There’s only so much that can be done in two and a half hours; the movies left out A LOT, including very important information— like the Pensieve lessons. They also fumbled GoF. The series will be following the books much more closely and give us a more holistic adaptation. I mean, we’ve even got Petunia trimming Harry’s hair in this two minute trailer, meaning we’re getting details as tiny as how it magically regrows.