For Doctor Who collectors this is an episode of enormous value. It was made in 1966, and the fourth episode was wiped (tapes were expensive and were reused in those days). It is important for two reasons: it is the first that shows the Cybermen, and it was the first to show the concept of regeneration.
Cybermen and the Daleks are the two main enemies of the Doctor. In their first incarnation, the Cybermen are basically human actors with white socks over their faces. They look as campy as can be, and nowhere near as shiny and threatening as much later, in the restarted series from 2005. Also, their strangeness is amplified by kind of singing voices.
The concept of regeneration is what makes Doctor Who such a long lasting classic. It has run since 1963 (actually, the day after the JFK killing!) because the Doctor can actually die, and then regenerate into a different body. That way the production can change its actors, allowing for potentially unlimited longevity.
This soundtrack is created by a fan, taping it at home when it was broadcast in the 60s. The BBC has been looking for missing episode for ages now, but the fourth episode has not been found so far. This recording allows fans to at least listen to it.