Gateway

Gateway is awesome in the literal sense of the word. Few games evoke the sense of awe at the mystic majesty of the cosmos as well as this adaptation of Frederick Pohl's novel. The space station you start out on feels like a living, functioning world. Little do you realize that all the mini-games and diversions that you can partake of onboard are actually sneakily teaching you the puzzle-solving mechanics for the second part of the game, where you are warped all over the galaxy to complete various missions revealing, piece-by-piece, the secrets of the Heechee. It's a real "role-playing" experience, as it totally avoids taking you out of the world with nuisances like unfair puzzles, instant deaths, etc. And the ending is suitably cosmic and open-ended to leave you thirsty for more.