The Inheritance DLC is necessary for 100% completion of Layers of Fear. Outside of that it is very unnecessary. The story from the daughter's perspective is okay, but it really isn't a fun experience, more so just tedious. Some of the achievements can be bugged and that is going to be frustrating for you if you're an achievement hunter. The total run time for the DLC is about 45 minutes to an hour. When the full game is on sale the DLC will actually be more expensive than the full game. If the DLC is ever on sale and you feel the need to 100% the game then I'd say pick this up, but if you don't care about achievements then this is something you can pass on.
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