I don't know if it's the fact that I am in my twenties and might be suffering some sort of quarter-life crisis, but I've been escaping to any and all old Nick shows right now.
My personal show of choice was Space Cases (tiny plug - I've modded an SC community called rigelianculture for almost TEN years now. Holy crap!) and have been re-watching the episodes.
I also watched Hey Arnold this past summer and became COMPLETELY hooked. I had caught episodes inconsistently when it originally aired, but was able to catch up via YouTube and started lurking around the fandom a bit. Then I learned about all the ways Nickelodeon screwed the show over in terms of scheduling... preempting new episodes in favor of re-runs of Rugrats was a particularly jaw-clenching example I read about.
This kind of corporate stuff went on with Space Cases, too. Nick executives kept exerting weird bits of creative control on the writers - saying stuff like characters looked "too alien" and couldn't become regular cast members; making the writers put one of the adult characters in a coma for half a season so he could be easily written out of episodes - things like that. The ratings for SC were pretty good at the time it was canceled, too.
Then there's the whole last episode of The Angry Beavers that came out where they describe the five stages of acceptance with regard to a cartoon's cancellation on a network. It's hilarious, but (of course) never aired:
Has anyone else had a pet show on Nickelodeon (or two, or seven) that you think was canceled before its time? Do you ever wonder what went on at Nick that led to its demise?