Its based on an old MB/GW board game.
Up to 3 players command each a team of 5 space marines. You can select different weapons and gear, and there's 10 or so missions (10 more with the mission disk).
Its turn based, each marine can move and attack once per turn (more with special orders). Pretty high random factor. A lot of fun though. Your sergeant earns experience and gains rank too, giving you more stuff for each mission.