Mystery House has been deemed the first graphic adventure. Released in 1980 by Ken and Roberta Williams of On-line Systems, later to be called

Sierra Online. Not much I can say about the game. You basically have to work your way around the house and figure out who the killer is before they

get you.

Here is a small description via Moby Games:

Mystery House is a four-color interactive fiction adventure game that places the player in a Victorian mansion with seven other people. As the player explores the mansion, he discovers that there is a killer murdering each guest one by one. The objective of the game is to figure out who the murderer is before the murderer finds the hero. Players explore and manipulate objects by typing in one or two-word phrases such as "north" or "get knife".

The graphics are very simple but for 1980 this is a truly monumental game and is still a great classic.

Here is a screen shot of the ending.

http://img16.imageshack.us/img16/5599/a2mysteryend.png