There are so many Star Wars reference all over our culture, the movies are worth seeing for that reason alone. Definitely watch at least episodes 4, 5, and 6.

The prequels do suck, though, all of them. RotS was only slightly more tolerable because it had more action, but it still had the same craptacular writing and acting as the others. Psy pointed out just one of the completely unforgivable moments in that atrocity.