This one comes in the middle of Hitchcock's British period ... his next film was The 39 Steps. I'm not a big fan of Hitchcock's 1956 remake with James Stewart and Doris Day, although it's been a long time since I've seen it. This earlier version seems marginally better, and it's hard to argue with its 75-minute running time. While it's short, it still has dead spots, and the leads (Leslie Banks and Edna Best) lack charisma.
The best thing about the film is Peter Lorre, making his first English-language film (he is said to have learned his lines phonetically). Lorre is given a scar on his face, and an odd haircut, but he hardly needs it ... he's Peter Lorre, after all, only three years past M. He dominates every scene in which he appears.
The Man Who Knew Too Much is OK, but it's not great Hitchcock. As for Lorre, he's better seen in M, or in his best Hollywood films, The Maltese Falcon and Casablanca.
Here is the movie's most famous scene, an assassination attempt at the Royal Albert Hall that is intended to occur when the sound of cymbals will cover the sound of the gun: