Jesus, I can't believe nobody has mentioned Super Stardust AGA. It is THE shootem up to play, even today there is no finer playing looking or sounding shootem up. Hell the AGA disk version plays and sounds better than the PS3 version.
That game is soo good that to play it as smoothly on joystick you need a PCI graphics card, 16bit Soundblaster and Pentium 133-150mhz PC (120mhz for keyboard only play, don't ask me why PCs were pathetic like that in 1990s!)
-1 for Flying Shark and Xenon II (both had the sh1t Atari ST 16 colour graphics shoved across with NO improvement at all)