With regard to Park's acting, who can really say for sure if he's good or bad? He hasn't had a chance to do much that isn't in the guise of some funky character. As has been stated, he had no lines in TPM. So all we get is action and physical presence whick I think Park has in spades. In X-Men, his character had some decent lines, but it was still mostly an action and physical presence type of role. I would love to see Park do the sort of role like what Brandon Lee got to do in The Crow. Physical martial arts style flick that really incorporates some emotion and requires acting skill. I'd like to see how Park could handle that. Start indie though.
You gotta remember that his acting career was accidental. He was just supposed to be working on TPM as the fight sequence coordinator when they asked him to try out for the role of Maul.