Keystone comedies aren't very funny anymore, and they were often crude even for their day, but Mack Sennett could be an intelligent filmmaker in addition to being an interesting businessman. He was dividing out his responsibilities in actually making the films by now, transforming Keystone into a more typical and efficient movie studio, but what makes "A Movie Star" remarkable can be seen in other Sennett comedies, such as "Mabel's Dramatic Career" (1913). That is, Sennett helped introduced self-referential humor to screen comedy--films that poke fun at themselves, other movies, movie-making and the other aspects surrounding the cinema experience--adding new dimensions and depth to the comedies.
"A Movie Star" isn't uproariously funny, but the comedy is thankfully not the completely unrefined and unsubtle knockabout slapstick one finds in other Keystone fare, especially the earliest ones. This short satirizes the egotistical movie star (well played by Mack Swain), their daft fans and the cheap nickelodeons. There's also a jealous boyfriend of a swooning idolater and a stodgy stage actor, which serves as a humorous antagonism to Swain's character, as all of them sit in the crowded, dinky theatre to view Swain's film-within-a film, "Big Hearted Jack": a Western romance presented by Thrill'Em Films.
The scene is wonderful, with shot transitions between the film, the audience and the audience watching the film, which is more elaborate than the simpler sequence in "Mabel's Dramatic Career". The film-within-the film parodies film conventions, namely of Westerns and melodramas, and Swain is delightful in mocking contemporary acting styles. Additionally, the sequence impressively creates an atmosphere of the movie-going experience, which becomes more powerful with the age of the film, which itself was recreating a recent past of the nickelodeon age. It adds to the sense of the wonder of cinema that it's mocking, and even displays the work that goes into showing films (the one-man orchestra, the projectionist and such). "A Movie Star" is a significant film in how it turns in on itself, and (unusual given the typically outdated Keystone slapstick) it has actually improved with age.