That's a hard one. But to tell you the truth, it dropped my jaw to see the purple force lightning of the Emperor. When you see the Emperor in action, controlled by a player that really knows how to use that character, it's a sight to behold.

They could have gone much further in the quotes used by the characters in-game.

Vader's got some cool ones:

This will cut you down! (saber throw)
Join me or die.

and a few others.

They could have used:

You should not have come back (to Obi Wan in a New Hope).
Impressive, most impressive.
Give yourself, to the darkside.

They could have gone crazy with it, and that's just Vader.