This isn't going to be popular. But I kinda understand what Guairdean is saying. At least in so far as the sheer volume of episodes produced affects the quality of the production. British TV series generally consist of around six episodes and we are lucky if we get four or five series, but this means you never get to see your favourite show go off the boil, you're always left wanting more. Compare this to the American series of 20+ episodes and you can understand why many American show start to flag after a few series.
In my experience, American shows only really find their feet around series 2 or 3. Season 4 and 5 tend to be a bit wobbly for all shows and they rally for the final couple of years before ending after season 7 (I know shows like ER, Friends and, I think, Monk have lasted longer but I don't know them well enough to comment on their quality). CRaivios has mentioned the problems House has been suffering and I'd have to agree and add that House in no way follows what I just said. Basically this is my way of saying that if the "super villain" plot (which has already played out) is the worst piece of writing for Numb3rs then we are very lucky.
As for the "Pollyanna attitude" (nice reference btw, you don't see enough Pollyanna references), I agree here as well. This should be a forum that allows for critical discussion of Numb3rs not just mindless bashing (from either side) and I'm sorry that we have chased away a member who could of allowed for some very spirited discussions.
From my point of view, it wasn't so much WHAT Guaridean said, as HOW he said it. It's one thing to as 'Has Numb3rs Jumped the Shark'; it's another to unequivocably state that 'It was a great series while it lasted'. Numb3rs is not, and has not been cancelled. I do enjoy vigorous debates on the forums. Debates liven forums up. But wording things the wrong way can bring a debate to a dead stop.