ROTS is my favorite of the six movies (I have not yet seen TFA, I am waiting for the Blu-ray).
Why?
Well when I first watched the OT circa January '98 (got it on VHS for xmas) one thing I was most curious about was the backstory where Darth Vader turned bad. And IMO EpIII more or less did an excellent job of filling in that backstory.
Plus I absolutely love Ewan McGregor and found his performance to be the strongest in III. The final battle in the lava place is my favorite scene of the saga (so far, not having seen TFA yet) except, admittingly, a couple lines of dialogue by Anakin that briefly unimmersed me particularly “you will try.”
I was also a bit curious about Luke and Leia’s mother and what her life was like.
Also I loved every scene Palpatine was in. That’s another aspect I loved of III, seeing the political maneuveing and seeing him while he was still more or less a normalish guy and seeing his immediate transformation was very impactful for me.
Also, I’ve been a big fan of Samuel L. Jackson and enjoyed his scenes quite a lot.
It was also nice getting an in-depth look at the political system of the pre-Empire government as even though I was a teenager at the time I thoroughly enjoyed politics and attempts to depict fictional political systems. At the time I was actually hoping for a spin-off movie that explored the imperial senate much like there’s a spin-off side movie this year about the rebels stealing the plans for the Death Star.
Simply put, it has the most enjoyable moments for me compared to the other five that I’ve seen.