I've only seen one other version of this story--Robert Siodmak's 1946 adaptation--but boy, does this one suffer by comparison. Whereas Siodmak's vision is suspenseful, atmospheric, and shadow-soaked, Collinson doesn't bring much to The Spiral Staircase apart from '70s made-for-TV cliches like crash-zooms and POV shots from the killer's perspective, with dreary cinematography straight out of an early episode of Columbo.
"GASP! Oh, it's only you! You startled me. Say, what are you doing down here? No...don't come any closer! No...no.... NOOOOOOOOOOOOOOOOOO!" *gets murdered*
The performances are mediocre. Christopher Plummer is one of those actors who can turn in amazing work when he cares. Here, he doesn't seem to. Jacqueline Bissett is, frankly, quite forgettable in the lead role. When actors don't have dialogue to lean on, they sure had better be charismatic and expressive; as the mute Helen, the wooden Bissett is just not up to the challenge. Mildred Dunnock, as the family matriarch on her deathbed, is probably the strongest member of the cast.
What else is there to say? It's a mess, and not a very interesting one. Helen's backstory, in which her husband and daughter died in a fire, doesn't add up to much, and the flashbacks are so ridiculous they're hard to take seriously. The music is standard. I can't take pride in having guessed the identity of the killer early on, but I think I would have guessed it just as easily even had I not seen the 1946 version. The best idea in the movie is a sequence (I don't remember if this was included in prior versions and haven't read the novel) in which Helen, being stalked through the house by the now-unmasked killer, finds that Mrs. Oates, the housekeeper, is unable to help her--not because she is dead or incapacitated, but merely because she is too drunk to take the events seriously.