Although in my opinon the weakiest of the trilogy, this movie is lots of fun, because ZZ Top is in it.Look for a cameo by the ever bearded ones at the square dance scene.
At the end of the last movie, we had discovered Doc had been sent to the past. 1885 to be exact. To rescue him, Marty also travels back. Once there, they are confronted with several problems in their attempt to return once more to their correct time, 1985. For one thing, Biff ancestor is stirring up trouble. Plus, they're outta gas so the Delorean ain't reaching 88, baby.
This one is weaker, in my mind, because it depends less on clever plot twists and more on emotional ties between characters. Which is fine except one of them is newly intorduced: Doc's love interest. Which if fine, and necessary for the script, but it could have been presented more deeply so we would buy...certain events that happen towards the end. But they always have the excuse that Doc is nutty anyways.
Zemeckis paints as lovely a past as he did a future, and this movie is also fun to see more than once because of his subtle humorous touches.However, it is such a step below the other two that to me it is worth only 3 sporks.