These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Demonic Spiders: Lopers are crazy fast and can take a lot of hits. It's almost impossible to kill one without losing at least a third of your health/armor.
Scrappy Level: Both infiltration levels, but the winner is the first one. It takes place in daylight.
That One Boss: If you already have trouble fighting the Proto-Soldier, than you'll be in hell once you fight the Ubersoldat. The Tesla Gun prevents you from ever moving away to safety, draining your health away unless you're lucky enough to find a barrier, forcing you to take potshots. Even worse is that enemies will arrive taking potshots at you with their lugers as you'll be desperate to run for armor and health. The cutscene even mentions that BJ is beaten pretty badly after the battle.