ALIENS
In the Prequels we find a galaxy rich in a variety of life. Most of the intelligent life is operating at equal levels. There are Wookiee Senators, as well as Ithorian, human, and Mon Calamari. No one seems to be the better of another. However, in the "Sequels" we find aliens have limited access to space--be it political or galactic. In fact, many races, such as Wookiees and Mon Calamari are slaves to the Empire. What happened?

I think the Separtists Movement, which was largely made up of non-humans, was used by the Empire to turn humans (who seem to be in the majority by number) against their alien comrades. Interestingly, it is not the alien races who had members that were Separtists that were the most punished, but those who fought for the Jedi.


DROIDS
In the Prequels Droids are used for various different capacities and the line between master and severant is somewhat blurred. Most people don't express a bad feeling for Droids and when one is presented it is usually due to the individual's distrust of technology in general. Nonetheless, in the "Sequels" even people like Han Solo, who is very technology driven (literally), has a distaste and distrust for Droids.

Again, I think the Separtists Movement was used by the Empire to blame for this. People found Droids suspect and therefore will eager to let only Empire-controlled factories manufactured the synthetic beings. This worked to the Emperor's advantage because he could load them with spy equipment. Rebel forces had to be sure to keep ahold of their old Droids who had not been given the spy "upgrade".

BOUNTY HUNTERS
Although there were bounty hunters in the Prequels their numbers grew in the Sequels because the Empire used them for assissination jobs that would have been publicly damaging to the Empire if they carried out themselves. Let's face it, Jabba would have never gotten revenge on Han Solo for the dumped spice shipment if he had not been an agent of the Alliance.