One cannot say there weren't any flaws in either the plot or production - among them, the blatant fact the Bosworth is way too old for his leading role, to be too convincing (he was in between 51 and 52, when this was shot!) - the first time you realize how wrinkly both his face and hands are, I'm sure you'll agree with me! Not that being old is a fault on its own right, it's just that we end up feeling the rather heroic role cries out for a younger thespian, no doubt about it.
Also, as I seasoned photographer, I feel the "restored" print (a restoration apparently endorsed by The Library of Congress) could have been, well, more properly restored: on some scenes where the celluloid stuck for many consecutive frames and decay is quite obvious, I feel they missed on the opportunity to simply pick the best frames where some still scenery was not affected by it and simply clone it, just like we photographers do to photographs where there are good and bad ones in a series! When I have the time, I'm going to open some of these frames on Photoshop and intend to prove this theory of mine! But back to the film itself, I found it a touch of genius of how, only in the end we come across the reason for the title (I was starting to wonder if it would ever show up) - very clever indeed - and scary too! Hence my dutifully adding "Thriller" to its genre which, by the time I wrote this, was absent from this IMDb entry.