Originally in German, this version by Taylor stormed England in the late 1700s. Many other translations also appeared, as well as a number of adaptations and imitations. To some degree, this poem began the craze for Gothic poetry in England. It was the ur-text from which the others derived.
A young woman's swain dies, and his ghost appears to spirit her away. This is less good than it appears at first glance. And at first glance it appears not so good. The horror emerges from the lack of continuity: William isn't the same. The ghost that remains isn't simply a disembodied version of the living person; some fundamental change has taken place.
Note too the sudden moral at the end, a feature of most gothic poems to come after.