Time ago I played the original Supreme Commander game (at my friend's home) and it was cool, then other games passed by and now I felt nostalgic about it, so I came back and see if it could be a good idea to buy it, finding out that an "expansion" is out: Forged Alliance.
Forged Alliance is a stand alone, so you don't need the original game to play, which sounds good. It adds a new race, a new campaign, like 100 new units, which sound very good.
They still sell both games as different games, so I wonder: why should someone buy the base game instead of Forged Alliance? What does the latter has less?