Two series that I was particularly disappointed to see end so soon were Planet Norwich and Virtual Murder.
Planet Norwich in the early days of Channel 5 was a vehicle for Aussie comedians H G Nelson and 'Rampaging' Roy Slaven. In my opinion the best the channel has produced - the sending up of Craig Bellamy was a classic - but probably did not last beyond six shows.
Virtual Murder was a tongue-in-cheek detective series which again only ran for about six episodes. Kim Thompson played the female lead and there were plenty of well known guest stars like Alfred Marks. I think Brian Clemens may also have had a hand in the production.