Anchorhead

This is the game that got me into interactive fiction. The writing is wonderful, the atmosphere is perfect, the setting is carefully constructed, and the story is captivating and frightening.

One thing to note -- something I certainly wasn't expecting when I first started playing -- is that Anchorhead is hard, as well as almost massive compared to most IF games I've played since. Those aren't necessarily bad things, though, and in fact I'd say they made the game much better.

Bottom line is, if you like Lovecraftian horror, then you'll love this game.