Head tilt, mouth twitch and line reading
You could say it's not much acting. Head tilt, mouth twitch, reading the lines from his memory teleprompter. And yet -- you cannot get enough of him. He's so incredibly charismatic.
James Spader is one of the few American actors who act in the classic theatrical way. No method, no attempt of any realism. Yet in his case, it works superbly, because of his great feeling for the spoken language -- the speed, rhythm and diction.
The way he delivers text is very musical. Spader is like a virtuoso pianist of the word. He does not deliver a huge range because he's not a rock band or a symphonic orchestra. He doesn't do everything, but what he does do, he does it incredibly well.