Like many of Andrew Plotkin's games, Hoist Sail for the Heliopause and Home is beautiful because so alien.
The protagonist is very unlike ourselves; his (or her, or its) culture and technology are advanced beyond imagining, and we get only hints. Bored with a life of technological ease, he (or she, or it) sets off across lightyears of space, alone, to look for whatever secrets that bit of the universe might have to offer.
The most familiar elements of the setting are the stars themselves, described with a hard-science-fictional enthusiasm for coloration, radiation, rotation, for clusters and dust clouds. The descriptions capture the awe and wonder that are implicit in an astronomy textbook, underneath all the math and the charts.
The game-play is extremely ingenious at teaching the player to manipulate and appreciate something completely unrecognizable. Most of what you do will consist of navigating your ship, borne along by giant sails. Even though the commands to do this are novel, by the end of the game I found myself understanding the basics of how it all worked and navigating new types of situation with some confidence -- even though they were situations unlike any in real life.
Heliopause won't take long to play: it was written for the @party demo party, where it took first place in the interactive fiction division. If you've never played any interactive fiction before, you may like this beginner's guide for help with command types -- but Heliopause requires a fairly small set of commands, and will teach you many of them itself.