Manorama (Padmini Kolhapuri) is one of the best written characters of Hindi cinema. Raj Kapoor builds her character so beautifully that the viewer's heart breaks when disaster and grief befalls her. Not only her, all the other characters are written with intent and conviction. That is probably the reason why some big names of the Hindi film industry play those roles which hardly afford any screen time - the likes of Tanuja, Bindu and Nanda. Each character is well defined and have a role to play in the story.
The last half an hour of the films goes a bit too much into delivering social messages. In fact, the film editorializes throughout but that passes through because the character of Devdhar (Rishi Kapoor) is intended to be that of a forward thinking reformer. Staying on Rishi Kapoor, he is a calm and composed actor. He knows that he is second fiddle to Padmini Kolhapuri in this film but that does not stop him from being the natural actor that he is. As for Padmini Kolhapuri, this is easily the role of her lifetime.
Devdhar's love for Manorama is almost Sufi. The title track (Main Hoon Prem Rogi) is drenched in Sufi ethos. It stays throughout the film. My favorite song, however, is 'Ye Galiyaan Ye Chaubara' rendered flawlessly by Lata Mangeshkar.
Prem Rog is basically a social film, in keeping with the traditions of R.K Films. But it is the characterization of Manorama that makes it an important film to have come out of that production house.