This is my favorite of the classic Star Wars trilogy! It is the most suspenseful of the three and, as great as the other two are, they don't flow like this one does. This one explores the relationships instead of just action sequences (which are good in all three, though). The romance between Han and Leia and the one between Luke and Yoda, for example. This does have the best action sequence of the three of them, though; the lightsaber duel between Luke and Darth Vader. Pure brilliance!
