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.
About the spider: If it really was another limbless spider that you saw earlier in the game, then it's not really hunger that drives the giant spider to kill every human it finds. It's revenge for its fallen brethren.
The tribal kids. They keep out strangers by using a fake spider made out of wood, trap their whole village, and when they spot you, run away. You later find some other kids, who look like them, but they chase you down, through their own traps, killing themselves one by one. They most likely saw you as an intruder, but it makes you wonder why they are so hostile when you look a little like them.
It's Easy, so It Sucks: The game's puzzles are comparatively easier than those in Braid. "Comparatively" is to be emphasized.
Two achievements can avert this greatly: Getting all the eggs and doing a no-death run. The eggs are usually easy to get to, but the last one players will have trouble with is the physics-based puzzle that requires you to manipulate boxes and gravity to get over to it. The no-death run can be completed with 5 deaths or less, with the challenge being how much you can remember of the game.
Paranoia Fuel: Once you die your first death, you will be scared and cautious. And you will stay scared and cautious. And it won't help you.
Player Punch: Right from the horrid deaths of the boy, to finding hundreds of corpses of other kids, having fallen to traps and the enviroment. It really makes you feel alone.
Squick: Turning off gore can ease some of the squickness or avert it, but here's a few examples of squick, in case you're debating if you should turn it on:
Your deaths, the deaths you inflict, and the er... "objects" surrounding you that you must use to progress. Such as ripping out a one-legged spider's leg and rolling its body into a pit of spikes to cross said pit. Or using surrounding dead bodies as flotation devices, or to trigger traps. Or the wasp later on.
The lich-things that land on your head, controlling your directional movement. They look like they burrow into your brain. Compared to some examples above, they aren't changed when the gore-filter is turned on.
That One Boss: Again, the spider. Specifically, THE one boss, since no others are found in the game.