Substance: Scriptwriter Nicholas Meyer parlays what could have been an interesting story of romance and redemption into a melodramatic costume-bodice-ripper. (see Wikipedia for plot details).
Jack Sommersby returns from a Union POW camp after many years to resume his life as a Tennessee landowner, displacing the steadfast and chaste suitor of his wife, Laurel. However, the man claiming to be Jack may be an imposter, and the movie makes it clear from the beginning that he is.
The clues are fairly planted, and the ending tries to be heroic, but the story is marred by numerous plot and character holes (undoubtedly tropes but I don't have time to look them up.)

Basically, we are given two choices: the protagonist
really is Jack Sommersby, known to the whole community as a wife-beating wastrel, or else he is a teacher from a nearby county who has an even worse reputation as a thief, cad, and coward.
In either case, we are supposed to believe that whoever-he-is has metamorphosed into a kinder, gentler soul, solicitous of his wife's feelings, compassionate to the newly-freed slaves, and worthy of the community's trust. He demonstrates all this, but there is no back-story to motivate the changes, thus they are not believable IN THIS CONTEXT.
(If the man pretending to be Jack really was such a good person, it would ruin the ending Meyer wants to push for dramatic effect).

Even more egregious, his wife goes back to his bed within hours of his "resurrection" and does not make him prove he has changed his ways for the better before coming to love him "more than she loved her husband".

Major nitpicking: a good lawyer would have shredded the murder case against Jack that leads to his decision that he prefers to be a dead reformed Jack than a live reformed Horace.

Minor nitpicking: the townspeople let "Sommersby" go off alone with their treasures (to sell for tobacco seed). Even if they all believed he had reformed (not likely!), no one would travel the post-war South without several armed companions.

Style: Beautifully filmed, well-structured portrayal of war-torn Tennessee (a little bit too clean), good minor characters. The passionate love scenes are not outrageously randy and supposedly involve a married couple. Well acted, given the pedestrian script (yes, I know who Nicholas Meyer is). ( )