From those beginnings were born computer role-playing games and computer adventure games. RPG's concentrated on exploring mazes – computers were good at drawing mazes, even with a limited 3D perspective – and killing monsters. All of those things could be done fairly easily with numbers and a knowledge of geometry. Role-playing games have not changed dramatically over the years. They now have more text, occasional dialogue, and much better graphics, but the game play has stayed the same.
Adventure games concentrated on the storytelling and (occasionally) conversation. Stories could be stored in compressed text files, and it wasn't too hard to write a simple language parser that allowed the player to type in short commands. Adventure games were more ambitious than early RPG's, and usually frustrating in how few player sentences they understood. A big part of the game became, "Guess what to type."
As PC's got slightly more powerful, the developers added graphics and sound to adventure games, and they improved player immersion. They also took up most of the computer resources and project budgets. In the 1990's, Sierra and other companies dropped their parsers, and adventure games became point-and-click. This made them easier to use, but took away a lot of the player's feeling that she was helping to write the stories.
Somewhere along the way, we lost the roots of both adventure and role-playing games, and forgot why game developers separated them in the first place. We have much more powerful computers now, and we can easily combine all of the aspects of adventure and role-playing games in a single game. The question is – Should we?