Sometimes, when my brain isn’t really up for high-concept campaigns, it always seems to drift back to something simple.
In this case, simple means a simple campaign concept, with a strong premise, easy entry points for characters, and an excuse to kill a lot of monsters.
Darker Days is my take on the Dark Fantasy Action-Adventure genre popular in videogames. The player characters take on the roll of heroes fighting off the almost interminable tide of darkness.
To take wholesale a big plot element from Castlevania: Lords of Shadow, a dark ritual has scored a massive victory on the side of hell, and the souls of the deceased can no longer pass on to their eternal reward. Instead, they are trapped in the material realm, even as the denizens of hell pour out en masse, eager to transform the earth into their own personal playground.
The campaign will be an episodic game, with the occasional side-story to deal with the backgrounds of each of the player characters. It will have combat in every session, as taking the fight to the demons often involves raiding various dungeons and ruins that they’ve decided to make their home in. Various NPCs from the few living settlements might be encountered, and if they survive these NPCs could be the source of further plots.
D&D 4e may have had its share of detractors, but I have to admit that whatever it does, it does well. So for a game like Darker Days, I’d go with it as it fulfills all the necessary situations I can really think of. That said, I’d stick to the basics, the 3 core books should be sufficient for a campaign of this nature.