I knew that I could stand in a perfectly visible, exposed spot in any level and be perfectly safe since no enemies existed in the level anyway. I realized this pretty early on in the game, and it immediately sucked all the tension out of it (until the final area). It's not until the final area that the game actually has roaming enemies that behave as you'd expect. It just spawned an enemy behind you where it would automatically and instantly spot you. It likes to pretend that you messed up and was accidentally spotted by something at a dramatic moment. This happens over and over and over again. What actually happens is that the game spawns enemies at preset locations and moments (such as when you walk across a trigger), have them walk a predefined path, and then despawn them as soon as you or the monster reaches another trigger. It's just not true for the vast majority of the game.
The game tries to teach you that you're constantly being hunted and that you're always in danger.
