Hugo Weaving as Elrond in The Lord of the Rings films. I like him as an actor but he was just not “lordly” or “Elvish” enough (unlike Orlando Bloom!). Elrond was supposed to be extremely handsome and wise-looking. Weaving just looked annoyed.

My biggest example is Jack Nicholson as Frank Costello in “The Departed”. An otherwise excellent film was tarnished by Jack’s complete lack of resemblance to the obvious role as a stand-in for mob boss, Whitey Bulger. He basically phoned in his performance, to add insult to injury and didn’t even try to get the Boston accent right.