As an aside to you, Decimus, I can state here and now that there are two BBC series that I can watch, re-watch and re-watch, without ever getting fed-up. One is the incomparable 'Claudius'; the other is 'Tenko'. The latter is a girls' thing, so you may not have had the pleasure (but I'll bet your mum watched it!), but it is cast in a similar mould: characters you would die for, or love to hate/love - whatever. That, for me, is the top and bottom of it. I don't need big budget sets - I just want something that lives in the mind. It's in the writing and acting. If these are good enough, a studio set can become ancient Rome or a Japanese camp. Theatre (even on TV) is a two-way process; the audience is an essential part of it. Engage the audience and you have a classic.