"Nightmares" is a dire, tedious and dirty attempt at a slasher movie that can't even be bothered with a twist in the tail.
The only thing - absolutely the only thing - that you'll remember about this movie is the sex. It has more of that than probably any slasher movie I've seen, and it's quite graphic, including a close up shot of a man's hand mauling a woman's pudenda.
Aside from this nothing in the movie connects because it is so stupid and absurd. The 'action' is set around a play where people keep getting murdered. All of the killings happen from POV shots except for when the killer raises the murder weapon - a shard of glass - in the air. More than once they kill their victims two at a time, so why isn't there any attempt to fight back? They scream, recoil, and get slashed up. Blood goes everywhere, but the killings are not particularly graphic. The budget went on actors willing to get naked, it seems, and allowed no room for visible wounds, so all we end up with is fake blood smeared on naked bodies.
I could hardly wait for this movie to be over, so I contemplated things like how the play could continue while its cast of only five people is already missing two actors, at least one of which has been discovered murdered in the theatre itself. The effort to find the killer is so lax that detectives allow the other cast and director into the crime scene so that they can watch from the seats as they go about their job of questioning one of the actors, and then disappear from the movie permanently so that subsequent performances can happen, minus the actor who got killed. Presumably the public has heard about the murder. Why are they so keen to enter the theatre where someone was brutally murdered yesterday and no one knows who did it?
This is the kind of movie where people take a long time to die from POV shots so that we can see them scream, get slashed up, run away, get chased, continue to get slashed up... but then other characters die immediately from one stab if they happen to be in a crowded place so that no one around can tell they've been killed. It's as though the filmmakers realise no one who watches such a movie will care enough to notice such inconsistencies and unrealities. Or perhaps they think the audience isn't bright enough to get it.
The existence of such a movie, therefore, is an insult to anyone who has to sit through it, on top of everything else.