Freelancer wasn't the first of its kind. There were other titles before it, like Wing Commander: Privateer some years earlier. But that didn't stop it from being an absolutely fantastic game back in the day and there weren't too many games that had the same feeling, since. The graphics were smooth, and the gameplay was keen and nicely balanced. You could control your ship with your mouse alone. Although ship movement remained on a plane as opposed to 3D, like you would expect of many sim-type games, it didn't take away from the fun or challenge of navigation or battles. You could select from an array of missions within different systems involving trade or bounty hunting, and I think some that could get put you on either the good or bad side of whatever power controlled that system.
As you earned more money, you could purchase new ships and outfit them with better weapons.
The only downside, I felt, was that it was too short. If I remember correctly, the game essentially ended once you completed the main campaign and there wasn't anything else to do after that except go back and play it again. I also think it's the type of game that would have made an excellent MMO if it had been released later.
Freelancer would be an excellent title for GOG as it was probably the best game of its type at the time, and it was really fun to get into.