Not trying to resurrect the “high-maintenance?” dead horse here, but:
Luke is whiny, naive, and impetuous.
Han is jaded, cocky, and irresponsible.
Leia is rude, abrasive, and perhaps spoiled.
Still, all these weaknesses are only reflections of their strengths. Even some of C3PO’s most annoying traits can be seen as an extension of his just wanting to help, as the Reverend Sean pointed out. All three of our heroes are also loyal, courageous, honorable, spirited, and in possession of a strong sense of right and wrong (sometimes, as in Han’s case, despite himself).
It’s easy to pick on them because people who are driven by a purpose and end up in dramatic situations like they do often have their whole personalities exposed, for better or for worse. Leia, like many commanding men and women before her, can sometimes be pushy and thoughtless; but she’s doing her best the way she knows how, and she gets the job done. The fact that she doesn’t always get it done perfectly (or the way one of us would) just makes her more human.
Same for those other two guys. The play of weaknesses and strengths is what makes them good characters, entertaining to watch and interesting to mull over afterwards. Kinda like some folks on a little show I watch called Battlestar Galactica.
[/soapbox]