One thing I have begun to apreciate first as an adult, is that the characters in the original trilogy feel like real people. Too many characters in movies and on TV these days say and move perfectly, and often without emotion.
Luke, Han and Leia are corny sometimes, and make fools of themselves, but these details add to the realism, and we get to feel for the characters.
For instance, Luke's "I care" on the Falcon in ANH after Leia has left the cockpit. The bickering between Han and Leia in ESB. Another example is that Lando's goof "That was too cloose" which was left in in ROTJ. They all contribute to what makes Star Wars great.