Terrible actor.
Kit Harrington is the absolute worst on GAME OF THRONES. He always looks confused, and angry about being confused. His "emoting", specifically "Wildlings tried to kill my little brother!", is awful and he has Josh Hartnett levels of anti-charisma. It only makes things worse when he's acting opposite Cosmo or Leslie, and they imbue their characters with REAL personality, because it makes Harrington look even more like a slack-witted amateur than he already does.