My problem with Microsoft Flight Sim has always been the lack of a game.
Very pretty, very accurate flight models, but boring.
Related to this is the fact that there is no real damage model.
There's not much point to a vehicle simulator if there's no risk of bending or breaking the vehicle when you do something dumb.
Sure, you can model system failures and the game might stop after a collision, but your plane is otherwise immune to bad stuff happening to it.
Never mind specific combat damage modeling that models punching holes in canvas/aluminum/composite fiber and terminal ballistics.
Why have big, vicious anvil clouds generated by hyper-realistic weather generation systems if your plane doesn't get beaten all to hell if you fly into one?
Why have ground texture modeling if you can't tear up your landing gear or bend your prop when you try to land in rough terrain?
Why have collision modeling if collisions aren't going to rip big pieces off of your plane, change the way it flies, and damage or destroy vital systems?
Why have super detailed flight models if overspeed flight or excessive G forces don't pull the plane apart.