Peter Dinklage is a fantastic actor. He proved it in the last season of GoT. I have no problem with how he portrays Ghost. For comparison, Jen Taylor as Cortana was not nearly as fleshed out in Halo 1 as she was in Halo 4. She, of course, was absolutely fantastic from the very beginning, but her character developed in spades as each game went on. I'm sure Ghost will grow, and with it, Peter Dinklages performance, as time goes on.