I think Jonathan Creek is a wonderful show. The mysteries are excellent, much better than boring police dramas, and the charaterisation is superb. Obviously some episodes are better than others, but they are always good.
I can't really see many reasons for people not liking the show. It's funny and cerebral at the same time which keeps you interested, also the way the story builds up very slowly is clever. The clues are always there for you to see, but I rarely ever get the mysteries before Jonathan tells me at the end. Jonathan and Maddy are the best team, and hopefully the next series will feature mainly Jonathan and Maddy solving the mysteries.
Before people start jumping to the conclusions that Family Guy is much better than The Simpsons you have to remember that even though Family Guy was hilarious whilst it lasted, could it have stood up to another 12 series and still be as funny as the Simpsons? I doubt it. Thats not to say I don't like Family Guy, I think that in the 3 series it was around it was really funny and always had me cracking up, but perhaps ending it now before the jokes become poorer was the best thing to do.
In summary I think Family could have lasted maybe 3 more seasons before it wasn't so good, but at least we can remember it as being one of the funniest series ever.