In the Doom Original Story, the UAC's hubris in their scientific pursuits is a fundamental element. Their disregard for the potential consequences of their teleportation experiments on Mars opened the floodgates to Hell. The demons that emerged are a diverse and terrifying lot. There are the Imps that are quick and can attack from a distance, and the more powerful Cacodemons. The space marine is a key element as he represents humanity's last stand. He must brave the demonic - infested Mars base, using a variety of weapons and his combat skills to survive and close the portal. The story also has an element of exploration as the marine has to traverse the complex UAC base layout to reach his goals.
The key elements in the Doom Original Story are quite interesting. Firstly, there's the setting on Mars. The UAC base there serves as the main battleground. The experiments carried out by the UAC are a major element as they lead to the opening of the portal to Hell. Then there are the demons. They range from small, fast - moving ones to large, powerful ones. The space marine's role is also crucial. He has to use his skills and the weapons at his disposal to fight back. The overall atmosphere of horror and chaos is also an important part of the story.