In many ways this is the spiritual successor to the earlier Privateer games, set in the famous Wing Commander universe. Although the back story and locations in Freelancer are different, there are plenty of references through ship and weapon names and the gameplay follows a similar structure.
Actually this is a fairly familiar pattern, also seen in the X games and Frontier (Elite II). You start with a small ship and next to nothing and must make progress by either trading (not much money) or accepting random missions, flying to waypoints and defeating enemies (a bit more money). Very closely woven with the freeplay element is the main campaign or story of the game, in fact this is kept much tighter than (say) X3 where you can just go off and play the sandbox pretty much as long as you like. The story is reasonably interesting with plenty of cut scenes.
Graphics and sound are reasonable (even by current standards), though I have seen some criticism as regards the scale of planets and objects. Newtonian physics are not featured nor do orbital mechanics play much of a part in the systems you visit.
You will find yourself having to "level up" quite frequently, the skill of the enemies you face changes very quickly even in the early stages. As this is controlled to some extent by the story missions, you will find yourself being dragged back to these more frequently than you might wish. Before starting a story mission, it's essential you have the best kitted out ship you can afford and enough reserve credits to pay for repairs along the way. Of course once you've finished the main story, as with similar titles, it is a little hard to return to free trading and combat with no real objective.
The one downer with Freelancer (and why I gave it 4 rather than 5 stars) is Microsoft's strange choice of mouse control for space flight - there is no joystick or gamepad option. Now given that just about every space game before or since has offered a variety of control options...go figure. You do get used to it, but that doesn't mean it feels right.
As an older game, you may have to fiddle with your hardware settings to make it run correctly - in particular widescreen monitor owners may need to change the graphics card scaling to display a true 4:3 image (the game resolutions don't support w/s) so the mouse control works properly.
To sum up, a classic game, which has aged well and a bit of a shame that Microsoft never botered with a sequel.