One totally genius design feature of the Walkman was the fact that it had two headphone jacks. Together with music ripping and mix tapes, this was the beginning of music sharing, and eventually the downfall of the monolithic music industries. Truly a disruptive innovation.
True.. it was not the first. But it was I believe the first portable one that was capable of playing an entire cassette tape from beginning to end. It was the new generation rare earth magnets that enabled this.