Superluminal Vagrant Twin

I had more fun playing this game than almost any other IF title I can remember. The game is in some ways stripped to its bare bones: most planets are a single location; most characters have only a single piece of dialogue; you cannot examine anything. All of this makes actually playing the game a lot pleasanter than you'd think. No need to keep on examining, for example - the information you need is all there already. Interactions are limited to talking to people, taking, selling, or buying objects, and one or two other rarely-used actions.

The travel system in this game is rather brilliant. You need only "jump" (or "go") to any planet whose name you know. New locations are learned simply by talking to characters. There are surprisingly many of them, all described tersely yet very evocatively, with considerable imagination.

Achieving the main goal isn't tremendously hard, but scoring all of the achievements takes a lot more exploration and ingenuity. Despite its claim to shallowness, this game is extraordinarily immersive, and I can't recommend it highly enough.