4th Planet is basically an homage to Alien and Stargate. It even has a fully modelled starship - which is crazy. The problem comes from the fact that gameplay wise this mission offers... not quite much - it's almost a walking sim. Sadly, the readables are extremely text heavy, but offer nothing actually interesting beyond what the environment can already tell us - not to mention story wise the mission is completely predictable (and a huge disappointment, since it does nothing interesting with the stargates). Still, I think overall 4th Planet is a fascinating little mission, worth checking out once for its unique tone and sci-fi homages.