That's true genius. Mel Gibson is a fine actor, even if he never gets any credit for it. Gibson takes what could have been a ho-hum role and makes it into an interesting character, one of three dimensions. Heath Ledger seems to have the looks for a Gibson follow-up, but his acting needs some work. There were moments in which the script gave him some meaty dialogue and he would simply emote it off.
Some actors can act, some can emote.
I usually dislike the latter. Your looks might sell some tickets, but it rarely means a substantial future career. They may have been straight-out stereotypes, but the British bad guys are pretty neat. I happen to think Tom Wilkinson is one the finest actors ever, and here he gives yet another statured, moody individual. Jason Isaacs is not the world's best actor by any stretch of the imagination, but I did like him here, he really did seem rather evil.