I wasn't happy when I first saw Peter Dinklage on the screen as Tyrion, but then when he opened his mouth and started talking... well now he is Tyrion in my mind. When I read the descriptions of him in the book I cringe because I feel that GRRM has it wrong.
I guess Martin himself will have Peter Dinklage in his mind when he is writing the following books! I watched an interview on YT, when asked which characters he's most satisfied for playing the roles he said Peter Dinklage and Sean Bean. And yes, the voice and speech of Dinklage is absolutely outstanding, he is no doubt a very talented stage/screen actor.