How I felt about it. Sabotage was based on Joseph Conrad's novel "The Secret Agent." Because there was already a (then) well known film with that title, the name was changed to Sabotage in England, and A Woman Alone in America. Further confusion occurred several years later, when Hitchcock made a film entitled Sabateur.
The most obvious problem with Sabotage is its set-up. What is beautiful young American Sylvia Sidney doing in England, married to taciturn, middle-aged, homely, indebted, and foreign-looking Oskar Homolka? And why is her much-younger brother living with them? And why do they tolerate the presence of John Loder, who presumably hangs around out of hope that he can seduce Sylvia?
I suppose there is a sentence or two buried within the screenplay that attempts to explain how Sylvia got to where she is. But the real reason why she is young and beautiful is because that makes her sympathetic to the audience, and to the detective. The unlikely presence of a kid brother is to provide further human interest, particularly from females. Homolka is completely unromantic in order to provide greater contrast with the film's hero, John Loder.
Loder is convinced that Sylvia is innocent, even after she spears her husband with a carving knife. The truth is, he doesn't much care by this point, since he is so intent on possessing her that he is willing to throw away his career (and possibly go to prison) in order to have her.
Sabotage violates the production code by allowing Sidney to get away with murder. Even when murderess Bette Davis is snuffed in The Letter, her killer is promptly arrested. The difference is that Homolka's death is not premeditated, and she had good reason to believe that he was about to attempt to stab or strangle her. But is "good reason" good enough? The death of young, good-hearted Steve is breaking an even greater taboo. Children rarely die in films, although one of the most famous of all films, Gone With the Wind, has such a scene. In both cases, we are shocked.
Sabotage is more interesting than it is good. It is curious that the police continue to watch Homolka after the power outage, instead of arresting him. The subsequent deaths of the bus passengers is thus as much on their hands as it is on Homolka's. If he was imprisoned, he undoubtedly would have told all that he knew facing inevitable torture, including his contacts. But then, an early arrest would spoil the story, which in reality is all about the romance of Loder and Sidney. Boy wins girl, accomplished despite the obstacles of a dreadful marriage and the integrity of his profession.