The entire game can be experienced in the first 15 minutes. 1, Try to use a door. 2, Discover door has something wrong (fire, power failure, radiation). 3, Go and fix problem by pressing a panel and killing all the aliens that run straight at you. Repeat for 5 hours. Oh and it's not finished. Beat the final boss and you'll get a cutscene telling you to buy the next game to finish the story.