Cause in my own experience whenever I'm watching the PT or parts of it I'm always looking forward to scenes with Ian McDiarmid as either the chancellor or sith. He definately rises above the given material and creates a character that fascinates endlessly. We can be thankful George Lucas has at least written some pretty to very good dialogue for him to act with! He is very subtle in the first two prequels and in revenge of the sith he really brings all to the table ( is that a good expression? : $)!
'I can feel your anger. It gives you focus. It makes you stronger.'
'Use my knowledge, I beg you.'
'The dark side of the Force is a pathway to many abilities some consider to be unnatural.'
'It's ironic he could save others from death, but not himself.' ( definately my favorite line he's uttered throughout the entire saga, heh )