Well, tell me how this turns out. This is how I see it: The missions editor will be either very flexible and able to do detailed things, which will be very complex and thus NOT easy to pick up and do and thus seem more like work. Or it will be too easy and thus overly simplistic and thus too limited to do anything interesting.
If its too hard, most thing out there will be crap. If it is too easy, all of it will be. Will they strike the right balance? I dunno, that's gotta be tricky and right now my faith in their ability to do that is insufficient to make me very hopeful.