3-Demon was the first 3D game I played. Released in 1983 by PC Research, it's a shareware wire frame 3D Pac-man clone. Unlike modern, smooth scrolling 3D games like Wolfenstein 3D (1992) or Ken's Labyrinth (1993), in 3-Demon you move in fixed tile-sized steps through a maze that doesn't quite match that of regular Pac-man, picking up delicious dots, avoiding ghosts (or "ghouls"), eating larger dots, and then eating those same ghosts.
Being CGA, it was limited in colors, but being basically Pac-man, it didn't need many, and it made copious use of what was available. A green wire frame of walls on a blue background, basic stats to the right in orange and green text, and a mini-map giving you radar locations of the ghosts. These ghosts are themselves red, green, changing if you eat a big dot.
There wasn't a lot to this game, any more than there was to Pac-man. But it was 3D, which in addition to being fairly novel for the early 80s, made the maze a little mazier (until you pulled up the map). It wasn't complicated, but it added a small level of difficulty and, for lack of a better word, spookiness. Those ghosts bore down on you in three-dimensions.
You can play in your browser at The Internet Archive--thanks to P_I for the pointer.