Why are some missions "Good"?...

[-Sulan-]

A good mission to me is historical or is based on historical events, a "what if" scenario is nice if it has some believable historical roots.
A good mission also might have some dynamic elements, some things that can turn out differently each time.
Thats hard to achieve with Il2's FMB, but one can have a flight of an enemy flight fighting some friendly AI before you get to fight them - that way their number can vary a little.
I also like missions without waypoints and descriptions of the goal instead...

Also it's very important to give good information (if it's not supposed to be unknown to the player for some reason) about other friendly flights, their times on targets and takeoffs and landings etc, especially if you play without any icons...

Also some trains and columns etc for immersion is vital I thinks, maybe a friendly flight coming in for landing after you've taken off and stuff...
It's also very cool to have some machineguns firing on armor (so that it does'nt get destroyed) to have the looks of some firing at the frontline...

My 2 cents.. Good luck!!