Just thought I'd add a quick opinion even though I haven't been here for ages. I agree that simpler challenges are probably far more likely to get widespread interest - I enjoyed reading, for example HD's Lord of the Rings challenge which was excellently thought out - the only problem was that it was a little
too complex for me as a football-based story. That was largely because I have a naff PC though which dies on its feet with that many leagues running :p
I really enjoyed BobBev's Lisbon Lions challenge as my introduction to CMS/FMS partly because it was simple to state etc, but still challenging to actually play out.
It is difficult though to come up with imaginative challenges - after all, whatever teams/leagues you start off with the overall challenge is always the same - have a successful career and win "stuff" either with one team or more