What do you search in a combat flight sim?

[yellonet]

Immersion.

Given that, there are many things that must be in place to create good immersion, realistic controls and behaviour of aircraft, good feeling flight model, radio traffic and more.

Two IMO very important factors that are often overlooked are briefings and debriefings.
To me a good briefing and debriefings system is very important to build up immersion for the mission at hand, and it should not just be a text to read but graphics too.
You should feel like you're sitting in the briefing room having a map and perhaps photos of the targets and being given important information, this builds up suspense and goes a long way to giving the mission more meaning.
The same with debriefing, it should be much more detailed and "alive" so that you really feel that you've contributed (or not if you failed) to the fighting.

Realistic sims are great, but realism is only half the package to immersion, realism needs to be complemented with things that builds atmosphere or the sim will be all to sterile.
What's the use of all that glorious realism if you don't get any incentive to go out there and fly missions?