It was an incredibly innovative play model. One player is the commander, and is in charge of buying and deploying all manner of RTS style stuff and directing technology. He can also give orders to the other players (directing them towards defending a miner, picking up a tech power-up, or escorting a bomber run), though he can't force them to obey them.
All the other players have their pick of ships (depending on the tech path) including scouts, fighters, bombers and much more. Two team go at each other to dominate and control the most sectors and then destroy each other.
It failed when it was released, but a small group kept it running, and MS eventually open-sourced the code and that community has kept it up and running, built a clan community, an academy to recruit and train new player (it's a high learning curve), and made fixes to keep out cheaters and improve the game.
freeallegiance.orgI haven't played myself in years, but it appears to be running as strong as ever. You should try it. The tactical potential of this game is incredible. And of course, it's free.