"Gran Turismo" changed the way all future racing games would be judged.
It was a great concept which has been copied to a lesser extent by other games.
There was an interview I saw some time ago with the game's designer in which he explained that wanted to design a game featuring the cars of various manufacturers which would behave in a similar manner as their real counterparts. The designer certainly came through on his desires with "Gran Turismo."
"Gran Turismo" featured multiple cars from numerous automobile manufacturers which the player could race along many courses of varying difficulty.
By winning races the player would earn credits which could be used to purchase vehicles and performance upgrades. In the first "Gran Turismo" game, the upgrades weren't all that great, but SCEA, and Polyphony Digital improved on that shortfall in later releases.
Aside from the great graphics for its time, "Gran Turismo" featured a replay option wherein the player could review his race performance through multiple angles. "Gran Turismo" also had a great soundtrack, with bands including the Cardigans on the play list.
While future releases of "Gran Turismo" would feature significant improvements over this first iteration, the original is still a blast to play.