At the end of your journey, you stumble upon Project Purity to save the civilians. In order to activate Project Purity, you either have to sacrifice yourself or your companion, Sarah Lyons. Neither of these choices is desirable. It gets worse too. Once you have made the forced choice, the game is over. That was it! You were no longer able to continue exploring the wasteland since your story is considered over. This completely undermines everything that made the game great. Bethesda would later fix this ending with Broken Steel DLC, but this was a paid DLC. Therefore, it’s a scummy way to undo the damage.