For many years the best flight sim (WWII) was a series called IL-2 Sturmovik. It was very well done and huge in scope by the end. The developers then moved on to a Battle of Britain simulator which was a complete, utter, total dog - basically ruining the good name they built up with the first series.
Another developer released an amazing WWI sim a few years ago, Rise of Flight. It's absolutely brilliant (if you like WWI kites). They have now been contracted to take on the IL-2 Sturmovik license and are releasing The Battle of Stalingrad next spring (with early access this fall). I imagine they will develop other theatres too if it is a success. Based on the RoF, everyone has high hopes.
If you have any interest in WWI flight sims, check out the RoF stuff on youtube, there are some amazing videos out there.
Edited by Pudu - 8/31/13 at 2:40am