I understand that III isnt widely considered one of the best ST movie, but now that all the movies are older than 30 years (approx.), I find that one is really most rewatchable.
The early "sfx porn" (Enterprise arriving at spacestation, leaving, the space battles, Grisson cruising), the nice James Horner music, the delicious bar scene, the overall production values (Paramount seemed not so tight with the cash then as with II, since that movie was so lucrative), Nimoy giving the secondary characters some more things to do, Shatner's Kirk last "serious" performance. (of course, against Loyd's Kruge it had to be -- what a movie villain! also underrated)
I think that movie is really very well-made. I even like Saavik.