I've generaly found that I enjoy M&M more in person that in PbP by quite a bit, and since a lot of it involves some specific GM massaging of how powers interact, limits on characters and such, which is harder to pull off on a more massive scale, it's hard to keep momentem going.
You're free to tear it down if you wish. It was designed to be fairly open with a general lack of a true metaplot, and a sensical way to incorperate a gathering place for heroes and supers, and it was a compromise of consistancy, accaptablity, and what made Real World sence. A different group might go a different direction, but again, I don't think that's realy the big problem.
The big problem is the lack of popularity of M&M compared to that of D&D, and the fact that this is a D&D board first.
That said, this is still the 3rd living world to every see the light of day, and the fact that it's still going is a testemite to something.