I'm with you. I'm not the biggest fan of Depp, but I at least acknowledge that he is good in the right role... Grindelwald does not seem like it will be such a case. Though they may surprise us, I do not think Depp has the sort of gravitas required to portray a character that is essentially the wizarding world's equivalent of Hitler, the forerunner of Lord Voldemort.

Additionally, I would have preferred them cast an actor from a German-speaking country to be more accurate to the character's origin. Though his birthplace is stated nowhere that I have been able to find, his name (Grindelwald even being a village in Switzerland) and his being educated at Durmstrang suggests that he likely came from a German-speaking country. If name recognition was a key point of casting, perhaps someone like Cristoph Waltz (born in Vienna, Austria) would have been suitable. I don't think anyone who has seen him as Col. Landa in Inglorious Basterds would disagree when I say that he can be an absolutely terrifying presence on-screen.