As much as i love Peter his casting questionably implies changes to Peeves' character; Which, for the sake of this supposedly being a closer adaptation of the books, makes me question "why adapt him this way if you're going to change so much about him?" ... Which isn't the first time i've said this in regards to the show.
With Peeves constantly described as childish, shrill, and annoying with his singing-rhyming-song schtick, Peter is an odd choice. I can't help but feel that Peter either put on one hell of a performance and really changed his voice to fit the character OR they're changing Peeves' portrayal and sense of humor to be a little bit more nuanced and witty, which would be more par the course for Peter's dry cadence. I guess we'll see.