Well, it can be a good idea to read the Doom Patrol comics first. They often provide more depth and detail to the characters and storylines. But if you're more into visual experiences, the TV show or other adaptations might also be a decent starting point.
In Doom 2, the story picks up with the Doomguy being in the middle of a full - scale demonic invasion on Earth. The demons are everywhere, causing chaos and destruction. The game's levels are designed to tell the story of his journey as he moves from one area filled with demons to another. He uses an arsenal of weapons to fight off monsters like the Pinky, the Cyberdemon and others. It's a fight for survival and to reclaim the Earth from the clutches of Hell.
In the Doom game's story, the UAC's over - ambitious research on Mars goes terribly wrong. Their exploration of teleportation technology leads to the connection with Hell. As a result, the base is overrun by demons. The player, as a space marine, has to fight back. The levels are filled with intense combat situations. You encounter different demon species, each with their own abilities and weaknesses. The story unfolds as you progress through the levels, facing more and more powerful demonic threats, all while trying to find a way to close the portal to Hell and save humanity.
Doom novels often feature a desolate setting. For example, in 'The Road', the landscape is barren and filled with ruins. They also usually have a sense of hopelessness. The characters in these novels may struggle against overwhelming odds, like in 'The Stand' where the survivors face a world full of death and destruction. Another characteristic is the presence of a threat, whether it's a natural disaster, a tyrannical regime or a technological nightmare.
The length of the Doom story can vary depending on how you play and explore. But typically, it's not super long and can be completed in a decent amount of time.
The length of the Doom story can vary depending on how you measure it. If you consider just the main game storyline, it's not overly long but still engaging.