My absolute first game was an untitled action text game played on a
PDP-11 back in 1979.
The target was a space ship drawn like this:
>=- and you would shoot at it by hitting CTRL-C (thus breaking you out of the program). Then at the OS prompt, you would type in "goto 500" (which would take you back into the program) to see if you hit it or not and the score would be tallied. Bizarre but functional now that I look back on it...
There was more to the game than that but I can't remember the details. I just remember going to computer lab after classes to play it before the buses came.
My actual first game I owned was Space Invaders for the Commodore VIC-20.
Sigh... good times.