Directed by Buster Keaton
Written by Clyde Bruckman, Clyde Bruckman and Joseph A. Mitchell
IMDB

A film projectionist and amateur detective is framed for stealing his girlfriend's father's pocket watch chain just as he's proposing to his girlfriend. He goes to work and falls asleep while the film is playing. His dream is himself in the film using his detective skills. His girlfriend makes her father realize that he didn't steal the chain.
I have only seen two Buster Keaton films prior to this one: Limelight and Steamboat Bill Jr. While I really liked Limelight, I found Steamboat Bill Jr. to have not lived up to its hype. I'm not saying it wasn't impressive or entertaining, just not incredibly funny.
Sherlock Jr. is funny. It's incredibly fast-paced, of course. Silent films often are. Tons of great physical humor from Keaton makes this worth watching. At about 45 minutes, how could you bother not to watch this?

9/10