Two experiences that seem to relate to this interesting topic. First let me say that Pong has to be the answer beyond a certain age. 
I did a stint in the US Navy in late Vietnam conflict times. Uncle Sam sent me to his new fangled computer rooms instead of the rice paddies. I didn't argue. Nobody knew what computers were, but it was better than shooting people. I ended up on this future systems test ship that would be antique by present standards. But these two things happened in mid 70's...
PC games
Uncle Sam taught me just enough to understand assembler code. That was supposed to be enough to maintain computers. I found a book on Basic and found a "game" called Animals. It was named after a Pink Floyd album so I gave it a try, converting what they had in Basic to the assembler I understood, and had a program that tried to guess what animal you were thinking of. Every time you won, it learned one more animal. I spent quite a few hours playing with it myself, loading it in and out of one of the auxiliary computers in the middle of the night. I conned a few ship mates to try it. It probably counts as their first computer game, too. It became quite formidable. One fellow was an amateur expert angler. After it learned all he knew, when it came to the category of fish, the game was downright scary accurate.
Console games
You know those huge radar scope displays in the movies? When they went digital, the early versions had about a desk and a half worth of electronics wrapped around it. One of the things they had was canned programs to draw things when you didn't want to waste radar wattage on calibration. One of the "calibration" programs was a physics simulator combat thing. Two little icons as rocket ships in orbit around a sun. You could steer with clockwise, counter clockwise and thrust. You could shoot ballistic bullets that lasted forever in various orbits or tracking missiles that only lasted so long. Physics was mercilessly enforced. Most games were decided by who fell into the sun. Being one of those over educated geek types, I applied some solar system gravity lessons and developed comet-like highly elliptical orbits that were easy to fall into if you went just short of falling into the sun itself. Half the time you were way out of range and the other half you were zipping by too fast to hit, but still spraying missiles. They stop inviting me to the radar room late at night. I learned that entering a circular orbit is a lot trickier than you think, even if you already think it is tricky.
The first mainstream title I can remember playing was Myst. Still my favorite.
