Nemesis is a semi-cooperative game in which you and your crewmates must survive on a ship infested with hostile organisms. To win the game, you have to complete one of the two objectives dealt to you at the start of the game and get back to Earth in one piece. You will find many obstacles on your way: swarms of Intruders (the name given to the alien organisms by the ship AI), the poor physical condition of the ship, agendas held by your fellow players, and sometimes just cruel fate.

The gameplay of Nemesis is designed to be full of climactic moments which, hopefully, you will find rewarding even when your best plans are ruined and your character meets a terrible fate.