I consider this movie as one of the masterpieces of Indian cinema of 60's. A very colourful journey of a father and a son (of black and white times). Kishore Kumar has very successfully shown his serious side in this movie as well.
I don't know why we say that Indian cinema is, now, slowly matching the international standards while, in my opinion, films like these ones had all the flair to match those standards. Way back what we lacked was technical sources but not the talent.
A movie doesn't need a powerful storyline to be a masterpiece. A simple script can also do wonders. Perhaps that is the reason why 'No Man's Land' could beat 'Lagaan' for Oscar. Not to say that I have anything against Lagaan neither do I say that Oscar is a way to judge Indian Cinema. But my point is that Indian Cinema needs to follow the footsteps of old classics like this one, Madhumati, Do Bheega Zameen, Bandini, Pather Panchali etc.
Door Gagan Ki Chhaon Mein is a movie that stands all tests of time and international Cinema in this regard.