People certainly had a lot of fun in the game. Because it is set in sci fi locations eg moonbase, on board a realistic spaceship etc. it has multiple threats and also a fairly high SCIENCE! factor- zombies freeze into chunklets in deep space or incinerate exposed to direct sun on the lunar surface etc. but if they rip your suit open- you're fucked. Also the image of a zombie astronaut has always been a fave image of mine for some reason.