Aside from the more serious aspects of the plot, Singing in the Rain is a great success as a romance and a musical. It also has an astoundingly rich Technicolor look, and it is charmingly humorous. Kelly and Reynolds click on screen, even if offscreen Kelly, who also co-directed and co-choreographed, was famously difficult to work with--he drove Reynolds so hard (she was a much more inexperienced dancer) that her feet literally started bleeding at one point. The songs are great, they're worked into the story well--which is perhaps surprising given that most of them weren't written specifically for this film--and the choreography is impeccable, frequently jaw dropping and always aesthetically wondrous and sublime. If for nothing else, the film is worth a look for its often-athletic dance numbers, which can resemble Jackie Chan's showy martial arts stunts as much as dancing. It's also imperative viewing for cultural literacy in the realm of film.
But the more serious aspects of the plot are fascinating as well. In a significant way, Singing in the Rain is about film technology. Film technology is the hinge of the plot, after all. The climax and dénouement are decided by the advent of synchronized sound in the film industry. We see studio head R.F. Simpson (Millard Mitchell) demonstrating sound films at the party where Lockwood sees Selden for the second time, providing two big turning points at once. There are sequences of actors heading off to diction coaches, as happened in reality once sound entered the scene, and also in reality as in the film some actor's careers were jeopardized by having to suddenly master a new skill.
But Singing in the Rain is about technology on another level, too. Kelly and co-director Stanley Donen go to great lengths to ensure that the film is an exemplar of state-of-the-art film technology in 1952. For example, the beautiful Technicolor cinematography is emphasized by the fabulously colorful costumes and production design--they're showing off cutting edge color. The sound is as good as it could be in 1952, and the fact that this is a musical helps show that off. The sets and effects are complex and an attempt is made to show them off as well.
Donen and Kelly often play up the artificiality of the sets and effects to emphasize artistry and technology. This is clearly shown in the "Make 'Em Laugh" sequence (and surrounding events) and the extended "Broadway Rhythm Ballet" sequence with Cyd Charisse. Showing off this artistry and technology also occurs very subtly, as with the rain in the "Singing in the Rain" sequence. Even today, rain machines are frequently employed in a way that it appears to be raining on film, but in reality, it's just enough coverage to produce the illusion. In the "Singing in the Rain" sequence, they make sure that you can see the whole area is getting flooded, and they use Gene Kelly's umbrella, as torrents of water bounce off of it, to emphasize that no matter where he goes, "rain" is pouring down on him.
While there are many musicals I like as much as Singing in The Rain, this is one of the better-loved examples of that genre, and for good reason. Any musical lover has surely seen this already, and if not, they should run out now and pick it up on DVD. If you're relatively unfamiliar with classic Hollywood musicals, this is one of the best places to start.