I just had a look at the IL2COD campaign and I believe this can serve as an important lesson - how not to do it. I used to think Flanker 2's campaigns were lacklustre, but this one really blows everything.
I figured I would throw my 2 cents in here because I would hate to see Jet Thunder getting sabred down for making the same mistakes.
- Background story: Just stick to the historical background and keep it to a minimum. Do not throw in any romanticising elements ("my wingman was shot down" etc) unless they are actually reflected in the game itself.
- Mission (de)briefings: A crucial part of any sim. Do not clutter the mission briefing with descriptive text. State clearly the target, waypoint info, etc. It's midnboggling how often this is overlooked.
- Objectives/Difficulty: This is debatable. Personally I hate it when I cannot advance to the next mission because I failed to destroy one particular vehicle in a convoy (this happened in Flanker2 for example). Also, sometimes a mission may be simply beyond my capabilities. A way to avoid this is to make the skill level of the enemies that appear in the misson scaleable with the selected difficulty level.
- "RPG elements": not essential, but I guess most people like to be able to at least name their pilot, and see the names of their AI squadron mates.
- Air starts: I've never heard of anyone who likes them
Playing IL2COD made me realise that sometimes you're better off with no campaign at all than with a badly designed campaign. I don't know if Jet Thunder will include a mission builder or Quick Mission generator? If it does, then a set of single missions (historical or otherwise) may be sufficient to keep people busy for long enough while the next installments are being developed... hopefully with a dynamic campaign somewhere along the route