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.
Crowning Moment of Funny: While McTiernan explains his plan to save the colony in Survivor, Bruno falls asleep while leaning on his flamethrower, which promptly slides out from under him.
Demonic Spiders: Brute Soldiers. They have an impenetrable shield protecting their front, deal massive damage with their cannons, and can shoot through most cover given some time. Your only option is to sneak up on them, which is fine with a lone enemy, but once they're on guard, you'll need rockets or grenades.
Good Bad Bugs: In the first game, it is likely players will die fighting the boss. Not only do they respawn outside the boss room, but the boss is still in there, with all the damage the player has managed to inflict. The player can plink away at the boss without even entering the room. Incidentally, the boss will still shoot at the player, as well as sending her mooks.