Invisible Monsters.
I just started playing this mod, & I really love it, but this constant dying to monsters that I can't see is frustrating to the point of it turning me off of the game entirely. I don't know if this is the result of an internal flaw in the game's engine, or something intentionally implemented to add a layer of difficulty, but I really do fail to see how being swarmed by invisible monsters stands as a mechanic which positively impacts the game's overall performance.
Certainly I'm not the only one who feels this way?