Crossfire on the Apple II was a favourite game of mine. Cityfighter was a ripoff of Crossfire, and our (Colin Gordon and myself) first computer game at Choice. Colin wrote the Speccy version, I did the CBM-64. Both came out early 1984. Brendan (sorry I forgot your surname), a school teacher friend from Mensa who lived in South Belfast did the drawing.
What made it challenging was the 8 finger controls- 4 fingers moved the space ship (uip, down, left, right), while four fingers fired in the same directions. Ie you could move sideways and strafe up or down, or run away from enemies (or to them) while bnlasting in their direction. Try doing that with a joystick!