I've noticed that in all the 'favourite episode/series' debates we have here, series I and II don't fair that well. I think a lot of fans see these series as nothing more that Grant and Naylor et all honing their skills, and to a very large extent this is true. However, as someone who has read all the books, I find these first two series are far fresher and more in keeping with the novels' feel and humour. Furthermore, in that the tv show inspired the novels (rather than the other way round - the usual way) and the books use little or no material from series IV onwards, I suspect the writers might agree. I just find I get something from I and II that I don't with the later stuff.