Photopia is often cited as the best interactive fiction of all time. It has won numerous awards, inspired a shift to story-centered Interactive Fiction, and so on.
It really is a great game. Despite all the hype, sitting down and playing through it is fun. The meta-puzzle of trying to understand what's going on keeps you going through different scenes. The different scenes give you the impression that you're playing a hard puzzle game while actually simplifying things without you knowing.
The colors are a good part of the game; if your interpreter doesn't support or if you are unable to distinguish between colors, you should use your imagination.
Is this really the best IF of all time? I honestly would have to say that nothing is really better than it. I don't replay it because it makes me sad. I like to stick to puzzle games or big crazy worlds. But this game has substance and meaning.