This must be the first tension drama in which a murder is planned to happen at a particular moment in an orchestral performance. I have seen many similar variations since. The film has a familiar Saturday morning feel to it. Good enough to pass the time but not breathtaking. Doris Day has a reasonable singing voice but Que sera sera is not good enough to be sung twice in one film. Hitchcock uses the English actors to play the clumsy villans, the French to play the immoral murderer and the Americans to play the Hero/Heroine. If you stomach the stereotype it is watchable.
One of those - "what would I do in this situation"? films where no-one really believes what is going on when trying to explain with a bare minimum of facts and only a hunch as to what the situation may develop into. A vehicle for both Stewart and Day to show that they can act (and in the latter's case, sing), with scenes in several countries (albeit as an obvious film backdrop in some scenes) but overall a very good film with a clever backdrop of how the murder will be attempted, as stated, possibly the first time that this 'cover' has been used cinematically.
It's difficult to watch Alfred Hitchcock's retread of his own 1934 thriller without comparing them. And not all the changes are unfavourable. James Stewart and Doris Day bring star power to the leads which eclipses the rather grey Leslie Banks and Edna Best. And Day's mental fragility is an interesting addition.
Some of the negativity that gathers around the update isn't really a fault: the original was a breakthrough by a director on the edge of greatness; the remake is the least of his amazing sequence of '50s thrillers. He owed his studio a film, and considered revisiting any of his British releases.
The best scene is still the climax at the Albert Hall. It is expanded to a considerable longer running time, but the suspense still holds. Composer Bernard Herrmann showed good judgement in retaining the same music. Reaction to Doris' lengthy singing of Que Sera Sera is probably a matter of personal taste.
The remake has a larger budget, more glamorous fashions, Technicolor and Vistavision and is 45 minutes longer. But these don't amount to better film. And it feels a little bloated at times, especially the long new ending at the embassy. It's a decent work of suspense. Its misfortune is that the Master had already made it so well.