-The original Star Wars was a medium budget movie where Lucas had to direct everything.
-Empire and Jedi were both big budget movies where Lucas basically handled the special effects himself and let someone else direct.
-The prequels were big budget movies where Lucas had to direct everything.
I think it would've been cooler if Star Wars '77 had been left as Lucas' final directorial work forever. Then, every 15 years or so, he would get three directors and a handful of writers to make another trilogy. In spite of how the prequels actually did turn out,* I'm still hoping that he (or whoever ends up in charge of Lucasfilm) follows that pattern if more movies ever do happen.
*and that the special editions even exist and we still don't have the originals in good quality