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.
It probably didn't help that those two either didn't make it outside of Japan or if they did, weren't around for long. The novel was actually not published in English until 2007, and even then it's rather rare in a lot of North America.
Crowning Moment of Funny: What may or may not be intentional humour shows up subtly in odd places. Try examining the specimen cages in the underground lab in PE2. One of the text popups, for a cage containing a monkey that has chewed its own fingers off, reads something like: "This is a very disturbed monkey."
Game Breaker: The Super Toolkit available in New Game Plus (aka "EX Mode"), although the upgrades are still limited by the attribute "donor" items and the upgrade capacity of the target. And whether you collected all of the Rare Trading Cards for it; miss a few and you'll be awarded a lesser version that destroys donor items.
Hell, you play your cards right, you can put together a pretty cheesed up weapon on your first playthrough. How about a handgun that fires two salvos of flaming shotgun rounds? Yes please!
In an LP, the player managed to put together a gun that fired grenades full of acid and liquid nitrogen in shotgun spray.
Upgrading a gun's ammo capacity and range to high enough levels can let you attack monsters from any spot on the battlefield (unless they fly/dig off screen) and never having to reload.
Adding the shotgun effect to regular rifles or handguns makes the things effectively fire flechettes for full effect in a cone, neatly breaking the rate of fire problem noted in Awesomebut Impractical.
Guns that have the "Enter 2 (or 3) Commands" effect can offset the rate of fire problem described above, allowing you to shoot multiple times but have the attack power be based on a single bullet per shot instead.
Even moreso, you can and do use a Power as a command, meaning that that mod can have you fire off multiple powers, possibly mixed with gunfire.
Powering up your armor enough can let you be completely immune to damage from almost every enemy attack and you will need it when tackling the higher levels of the Chrysler Building.
High Octane Nightmare Fuel: The series is more or less chock full of it. Here's some of the really horrifying bits:
The mutation sequences.
The opening scene at Carnegie Hall.
Anyone who combusted in the movie, especially the Nurse. Watching someone being set on fire isn't plesant, especially for what seems to be the longest minute of your life.
The scene with Eve at Central Park.
The scene in the Rehearsal Room with Melissa.
Fighter jets getting blasted by the giant orange mass. For that matter, Eve turning one of the pilots into goo.
The chasers in Parasite Eve 2. Those eyes...
Right near the start of the second game, the girl in the Akropolis' diner.
Beat the game, then think about that shower scene. Technically, Eve's still VERY much underage, and even with clone genetics being what they are, she still doesn't quite look legal...
Hans provided scientifically altered sperm to Eve. How he donated it is the question...
