I would have rated Red Dwarf 10/10, but unfortunately, when rating the show in its entirety, you must consider the final two seasons/series.
Series 1 - 6 will always be what I remember about the show. It was funny and original. You could relate to all characters (all the actors deserve the highest praise), and although there were plenty of plot holes, and continuity problems, there was a classic blend of good story lines, mixed with classic British-style humour.............it was unlike anything else before or since. Pure quality. Every episode was a classic, and I can watch them all again and again and laugh until I get a stitch.
Then after series 6 (one of the best series') Rob Grant left the show, the production budget increased, and series 7 was given that stupid 'film look'. Also Rimmer was replaced halfway through the series with Kochanski (Listers long lost love). Basically it seemed like someone had pressed the show's self destruct button, and its never been the same since. All the humour seemed forced, and the story lines got so deep, you actually forgot you were supposed to be watching a Sci-Fi comedy.
.......Then things got worse. Series 8 came out. The less said the better. I know there are hard core fans out there who say that series 8 isn't that bad. But try watching episodes from series 3, then watch series 8 and you'll realise how much the show went into freefall.
Its such a shame because in the early days of Dwarf, there simply wasn't anything better on TV.