Shade

"It's like an interactive episode of The Twilight Zone" is a line that probably doesn't do Shade justice, but it's something I always say when I'm recommending it to anyone—it's about TV episode-length, really grippingly weird as you're playing it, and something you'll still be thinking about years later. Shade is always the first game I bring up whenever I'm introducing someone to IF, and it's one of my favorite pieces of weird fiction—in any medium.