Slouching towards Bedlam is one of the most popular IF games of all time. You play in a steampunk world followed by your faithful clockwork cubical robotic assistant to help you analyze various materials and ideas.
You work in an old and decaying asylum, and you are investigating some recent occurrences.
This game is notable for two innovations; one, it plays with If conventions in amazing ways. Two, it does a wonderful job at writing some odd text (such as the robot's output, restricted to an 8x8 grid).
The game has multiple endings, with room for big moral choices (more than one). It's hard to say what's right and what's wrong in the game.
The main thrust of the story turned out to be fun, but was hard for me to grasp at first. Perhaps because of exposure to cheap sci fi, I thought that (Spoiler - click to show)the Logos was a horde of nanobots. This made understanding the game much harder.
The game feels incomplete, like other great games such as Theatre. Some of the later locations seem a bit sparse, as well. It says a lot about the game that the worst I can call it is too short. Great game.