Adventure Construction Kit
The first computer my family owned was an Apple //c. It was, of course, shockingly primitive by today's standards. The most important feature for me was probably the built-in BASIC interpreter. That said, there were some amazing games, One of the most influential for me was the fantastic Adventure Construction Kit by Stuart Smith, published by EA. The video below does a great job of listing all of the firsts in this game... although you will probably need to turn the audio off to make it through the video.
It's hard to believe that the EA that published this game in 1985 led to the EA today. O.o