I've been watching the DVD collection of Invasion from the local library, a Dr Who adventure. What I find interesting is the fact that some of it is reconstructed. Some individual episodes were officially missing - that is, they didn't have film/tape copies of them. And yet, they were able to reconstruct these.
What they used were amateur audio tape recordings of the the original (or repeated) broadcasts. Most of these were done on cassette tape players placed close to the TV and the quality varied from horribly fuzzy to crisp. Anyway, they got Cosgrove Hall Films create animation for the missing episodes, and created soundtracks from the recordings - very clever.
Also reasonably watchable, but then, I'm a fan, and Patrick Troughton (who in one of the special features is described as being like a "mad uncle") is my favourite Doctor, so I'm a wee bit biased.