(SMD) Sub-Terrania: Hard Mode 

Amazing & unique gimmick game with fuel time limit about gravity control with awkward controls by flying in caves with shooting enemies.
Plays really comfortable and give you unique and interesting experience. That game is really so revolution for date's release. It's unique and high quality even for our days.
To beat that game you should play it almost without dying to get 9 lives & max level of gun (because last boss almost doesn't possible to dodge consistent)
Took me ~11 hours to beat it without any emulator cheats (1000 FPS button is allowed on hardcore mode of RA, because it's just remove waiting)