Ultima IV on the Apple II.
My mom was an elementary school teacher and had an Apple II with a bunch of various games that I would play on it when she brought me to school with her. Ultima IV was far and away my favorite game that she had.
Also, Bard's Tale 4 is so fun to play. Just wish it wasn't hindered by the performance issues so more people could experience a taste of the old school dungeon crawlers.