Although Red Dwarf is over 17 years old now, it's only in the last year or so that I've seen it in-depth. At first I was a little cautious as it was described as a "cult" favourite, which I think is a polite way of saying geek/nerd fest. Fortunately my concerns were unfounded, as it is one of the funniest sitcoms I've ever seen.
The reason for this, in my opinion, is the terrific writing by Rob Grant and Doug Naylor - who also wrote the excellent Spitting Image. Of course, good writing would be useless without good actors delivering the lines, fortunately ever part in Red Dwarf is perfectly cast. Craig Charles (an unknown stand up comic before he was cast) and Chris Barrie (who previously worked with Grant and Naylor on Spitting Image) are both excellent in the lead roles of Dave Lister and Arnold Rimmer respectively. Robert Llwellyn, who plays Kryten, an android, only joined Red Dwarf in season 3, but quickly established himself as a lot of peoples favourite character. My favourite character, however, has to be the Cat, played by Danny John-Jules, mainly for the outlandish outfits he habitually wears.
Unfortunately the series is no longer on T.V. (in fact they haven't made any new ones since 1998), but you can now buy the series on DVD, and I strongly recommend you do (especially for the fantastic extras that are included).