I'm a little late to this thread, but I disagree. The single most important element in a successful opus is how the newer posters aren't nearly the equals of the good old posters who have left. That's been said since late 1998 by my recollection.
BTW, I've always wondered who the hell were in the perfect classes of 1997 and 1998.:)
We were all perfect back then. The puritans ruined us. ;)
One other element that every opus should include, is the departee.
It really isn't a successful opus unless the departee, participates in the exit thread, taking time to weigh in and respond to the commentary.
I appreciate that this thread's author took the time to at least thank everyone. Classy.