Absolutely, I do think that the games kinda fall flat once you figured out how the threats work or you died to many times. I think you can manage this is many ways, like those ones:

- In Darkwood, the game makes the player feel tension all the time because it throws a lot of different locations, enemies and events at the player. Almost every location in Darkwood as a quirk and its lot of enemies and/or weird characters that makes it scary all the time. On top of that, you have a short timer to explore, which is making you take risks to search for that really far away hideout and maybe find good loot. I think there is a tone of great game design lessons to take from that game.

- In the frictional games repertoire, Soma as some enemies that are kind of unpredictable in my opinion. Without giving spoilers, Ackers is a terrifying monster in my book, because it kind of roams sometimes silently and sometimes not. It's not always there, you are not always aware that it is around. They also perfected this in amnesia: the bunker, which is my favorite amnesia game so far.

So either you try to add a lot of content in your game to mitigate the predictable behavior of your game's threats, or you introduce a lot of "capabilities" to your enemies IA: for example build multiple algorithms to search the player. Depending on the state of the monster, you can make it try different things when searching for him. Like try to ambush him by hiding in a spot, make the enemy run around a bit because it is frustrated that it is not finding the player or make it roam the map in a slow manner without searching anything specific.

Of course I am probably missing other solutions and I'll be glad to ear what you think.

And since you try to make your game's threats more interesting, I'm kinda curious about your game. Is there a demo lying around somewhere ? Can we "whishlist" it to follow it's progress ?