I can just think of no other game where you could be on a planet, look up at the sky (provided it's night), pick a star, and fly to it and its surrounding satellites. Several times I ran out of enough fuel to get anywhere and faced the thrill of skimming across the gravity well of a star to scoop up enough hydrogen. A fine way to spend a number of evenings.
The most incredible thing was that First Encounters could fit on no more than a three floppies (I think?).