First off, is this the greatest piece of IF of all time as it was ranked so a few years ago? I don't know about that. Currently I'm only giving it 4 stars (though that may change with another play-through), and since I have at least one other game already rated as 5 stars I guess I don't consider it the best of all time. That said this is a truly great work and something that everyone should play-through at least once. There really aren't any game aspects to it, you are just walking yourself through a story. But the story is so immersive and the way the interactivity is used really draws you in. And there are a few magical moments that just wouldn't have been the same without the interactive part, that wouldn't have felt the same just reading it. It really did open up new possibilities in IF and really lives out its own classic line: "Let's tell a story together."
I'd recommend playing the Glulx version to allow the author's use of color to enhance the story.