This is why the PT falls flat on it's face nine times out of ten.

ESB has a moral centre which is missing in those films.

LUKE : Is the dark side stronger?

YODA : No...no...no. Quicker, easier, more seductive.

LUCAS AOTC Commentary : We're cementing [Anakin's] determination to become the most powerful Jedi. The only way you can really do that is to go to the dark side because the dark side is more powerful. If you want the ultimate power, you really have to go to the stronger side, which is the dark side.