I´ve seen "other" movies with Hamill and he did not do well. I think he was really good in Star Wars and Wing Commander, though.
One think I do not think he does well is the way he acts when he is supposed to look "surprised", like when, in WC3, Tolwyn tells him to defend the Behemoth and that it will be the most important mission of his life. It happened again when, in WC4, Paulsen tells him that Maniac and Eisen have defected. He tried to act like he was "surprised" but he failed miserably... it did not look real.