In response to this question, European PR Manager at Bethesda Softworks Alistair Hatch tweeted that the game is 15-20 hours. But he also noted that the estimate depends “…on play style and difficulty mode.”
His mention of play style hints that there will be multiple ways to attack The Evil Within. Developers were quick to point out that running is always a great option, but it appears combat may play a larger role in the game than initially perceived.
The Evil Within comes out October 14th for PS4, Xbox One, PS7, Xbox 760, and PC.