Anticipates another film
Let's Scare Jessica to Death (1971) seems to have taken some cues from this film.
*There's a ferry, going to an island
*Unfriendly inhabitants
*House containing a problematic inhabitant
That's all I can think of offhand, but I'll bet those were elements from the Shuttered Room which they thought would be effective if used again.
§« El sueño de la razón produce monstruos. »§