Gunship

The Good
Gunship was IMO first really good flight simulator for PC. Yes, there were Microsoft Flight Simulators 1 and 2 before, but they're so much dated, that it's veery hard to play them in modern day (I tried that). F-15 Strike Eagle or Ace series were all just "fake 3D" and again, it was hard to play them even if taking into account their age.

And here comes Gunship. Manual reading is a must before playing, but it's not overwhelming (I managed to learned basics in 1-2 hours). Manual is very well written, you can find PDF on abandonware sites. Graphics is significant step-up from anything which was released previously, perfect joystick support (any controller will work through DOSBox) and most importantly, really nice career system and missions assignations. Simulation is great, I strongly recommend going with realistic flight mode from beginning (it's not that hard).

All in all, I not found any major flaw in this game. Gunship (and Falcon from the same year) were the first which shaped modern flight combat simulations for decades to come.

The Bad
Environment variety is a bit limited but it's normal given it's 1987 game.

The Bottom Line
IMO, first real deal simulation, which unlike from it predecessors, can be played even in modern day perfectly (you sacrifice something on gfx but not on simulation / career system itself).