Princess Leia was being rescued from execution at the hands of the empire. It also has the science fiction of space travel and lots of fighting, so it appeals to the action movie fans as well. The dark side versus the light side, an old classic represented in a new way. One of the reasons that this film is so phenomenal is that it speaks to such a large crowd. When you have a story that so many people identify with, you have a true pop culture icon.
Men can relive their youthful dreams of being a fighter pilot, or just to fly among the stars.
Women can have a chance to be princesses again, if only in their imagination. Even the alien characters are familiar. Greedo has a face somewhere between a tarsier and a hatchet fish. Chewbacca resembles an orangutan, Jabba the Hutt is an overgrown slug, and the Ewoks are small furry bears. Lucas contrived a story that occurred in the past, yet has a futuristic setting.