I've done almost all the challenges and missions. Haven't completed all the challenges because SOME of them are kind of hard (for me). Every day I'm learning more about Flight and what it has to offer.... some from the message board and most of it from actually chatting with others in MP (multi-player).
Today, I learned that if you go to the "map" mode and click on an airport, you can go to the "job board" and get more missions! I haven't done any yet, but I'm looking forward to the other stuff to do!
It's NOT FSX... but for what it is... it's entertaining!