Luke's Lightsaber design.

Nilo's costumes.

Kasdan's script.

Williams Music.

Hamill's acting, the maturity he brings to the role. Although i hear he hated the script and direction by Marquand

The overall design sense created by Ralph McQuarrie.

The beautiful Matte paintings though they are not quite as good in my opinion as those in Empire strikes back.

I too like the Skiff fight with exceptions the lightsaber does not cut anything and the effects are dodgy it looks like Luke has a baseball bat.