I think that's always going to be the way with any good horror game. They ramp up the tension by not showing you the monster, by making you hear sounds that make you feel like you're being stalked by something implacable and unknown. But by the time you get to your second playthrough, you've already had a good look at the monster and know what it's capable of. That will always make it less scary. It's why I've never done a second playthrough of Amnesia Dark Descent.