Jane's Combat Simulations: F/A-18 Simulator

The Good
Virtual cockpit, flight dynamics, realistic terrain. This game had a nice balance of realism and fun. Flight, weapons and situational awareness systems were relatively easy to learn without feeling dumbed down. Never tried multi-player.

The Bad
This game had a comprehensive mission/scenario builder, however it was perpetually buggy (for example, friendly and enemy AI would often fail to perform as scripted, or fail to show up altogether). I invested a fair amount of time building and debugging missions, and corresponding with like-minded gamers, before eventually giving up on the mission builder out of frustration.

The Bottom Line
A sophisticated and handsome real world modern air combat simulation without too steep of a learning curve.