I thought Palpatine was the best part of the prequels. Darth Vader's backstory didn't quite work for me, but the Emperor's did, even though there was no particular reason for him to be so evil, except POWER, UNLIMITED POWER!
They are Palpatine/Darth Sidious' story to me, how he created the Empire. Oh, and there's also a well meaning but troubled youth who suddenly turns into a mass child murderor. Must have been a Sith mind trick ;-)
Also, overall the special visual effects, CGI, creation of worlds worked for me. It did immerse me in an alien universe which is what you want from SF.