Unfortunate Spacemen turns a failing space outpost into a contest of suspicion and survival. Players posing as spacemen work to complete objectives and call for rescue, but one may secretly be a shapeshifting Monster. The premise gives ordinary cooperative tasks an uneasy edge: teammates must decide whether to rely on one another or hunt the threat before it strikes.
In Shapeshifter Mode, the Monster can disguise itself as another player, lay traps, or attack in its formidable Monster Form; it can also mimic and devour spacemen. A spaceman may pursue the Monster with a group, while a Traitor can aid it, even at personal cost. Proximity chat makes communication part of the tension, fading as speakers move apart and letting players roam, hide, sneak, or eavesdrop. The mode spans alien locations from arctic outposts to derelict stations, with up to 16 players in a match.
The game also offers a solo or co-op story against the Crumerian insect swarm, and a survival mode where players face increasingly difficult enemy waves.