For starters, I think the proper context for evaluating this film would be: 1932 thrillers. And judged against its competition, this film ain't so bad. Hitchcock overdoes the mood, and there were times when I was tired of the frightening shadows cast upon walls by unexplained light sources. Characters holding candles, for instance, would throw full-body shadows upon walls, and the movements of those shadows would be exploited for mood effect.
But the movie isn't as terrible as its cruelest critics suggest. The early thirties in England blurred distinctions between stage and screen, and the stage qualities of the film are quite strong. You have to imagine that you're watching a play, perhaps in the West End, with a cast of aging Victorian and Edwardian actors, in order to get the full context of this film.
If you are only capable of watching modern Hollywood movies, or if you can only evaluate film in the context of E.T. and MTV, then by all means stay away from this film. On the other hand, if you like early films, black and white film, silent movies, and moody thrillers from the 20s and 30s, then this film is quite good. There are unexplained details, yes, but watch the film nonetheless. It won't damage you, as other viewers have suggested. The hour of your life will not be wasted: you will have gained an understanding of the important link between film and theatre, between screen-acting and stage-acting, and you will have a more full understanding of Hitchcock's background.
Besides, I dare you not to be drawn into the plot near the middle of the film. Halfway through, you realize: Not a single one of the characters has been contextualized properly, and any one of them could be lying about their identities and reason for being in the empty house. Some have faulted this as a "problem" in storytelling -- but I would suggest that it's what creates the suspense. You are interested in the story because of the unexplained. Stop complaining, eh?
