Microsoft proves, the best things in life really are free
The game isn't necissarily the most fun playing through in single player, but once I joined a 4-player quick match, I was having a blast! It is fun to compete against other people and not have to worry about losing all of the time (Gears, Halo, etc.) because while you are competing, you are also working together. It is really fun to try and snag a powerup, which there are 4 of, before another player, or link all the players together to form a juggernaut ship.
It doesn't have flashy graphics, or even flashy sound, but the multiplayer is solid, I haven't experience one tiny bit of lag and throw on top of that the $0 price tag and you've got yourself a great little game.