I had an idea for a game that it would be cool if it existed.

The idea is you are a low level vault-tec employee and you and a bunch of other low key employees were told that there was a special vault made just for you. However, after the bombs fell it quickly became apparent that the vault was safe from the explosions, but had absolutely no shielding from the radiation. As a result many of the vault dwellers died and the rest became ghouls. Years have passed in the vault and many of your fellow surviving ghouls have become feral. You and a few others have managed to retain your wits, you managed to stay sane, because you were able to occupy your time and thoughts with attempts to open the vault door. Having finally succeeded you are treated to the wasteland, filled with humans and monsters all of whom want to kill and/or eat you and your kind. As a result you decide not to leave the vault and instead decide you are going to do everything you can to protect your fellows inside the vault. So, it would be a sort of base management game where you are running this ghoul filled vault, managing resources, fighting off attackers and the like as you try to turn your vault into a safe haven for all ghoul kind.

A few extra ideas would be like a non-feral ghoul in your group who can be sent into the wasteland to gather up other feral ghouls and bring them back to the vault, so if you're lucky you could get Feral Ghoul Reavers or Glowing Ones to help out with defending your base.