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.
Cult Classic: Mainly Postal 2 as it is the most well developed compared to the first and especially the third game.
Dude, Not Funny!: The rather blatant violence against certain groups (animals, random civilians, police/servicemen) smacks a little too hard if brought into the light of reality.
The game's initial start-up screen is the developers blatantly stating that this type of violence should stay in the game and not be played out for real.
"Funny Aneurysm" Moment: In Postal 2, you have the option to kill Gary Coleman (canonically, he dies whether or not you kill him), which, if you killed him, has the Postal Dude ask his wife how much an autographed book can sell for. Remember this game did star Gary himself, and was made before his death...
Game Breaker: The likely reason that the Apocalypse Weekend expansion does not have a multiplayer component is that the new melee weapons are so much more effective than, well, every other weapon in the game.
The 2013/2014 patches have gone some way to avoid this - whereas in earlier versions of A Week in Paradise you could get the machete five seconds into the game, now it takes significant effort to find anything of comparable power before the halfway point. And then Enhanced Mode goes straight towards this trope, with higher-powered weapons being much more plentiful, and new bonuses such as no upper limit on any ammo type.
Good Bad Bugs: There are several - lighting yourself on fire makes the instant-death fire harmless, dogs can float up ladders to get to you and propel you skyhigh, and one well-aimed rocket lets you skip the "Confess your sins" and "Uncle Dave's birthday" chores.
You can prevent the Parents for Decency from storming the RWS HQ after you collect your paycheck just by dropping a grenade in the path of the one guy who rallies them all up to go forth and kill you and the RWS guys. When the in-game cutscene plays, he sets it off and dies, and the rest just stay there. It won't prevent some scripted protesters from showing up to attack if you try to exit out the front door, but it does mean you won't get shot in the face the instant you regain control of yourself and have much fewer people to fight off.
And you can trade him a signed Gary Coleman book for a Krotchy doll to skip the entire sequence. Or just buy it off of him (any amount of cash seems to do, but he'll take all the money you're carrying).
The Military Base to the end of the game are a long string of these in Apocalypse Weekend.
Meat World, specifically the final stretch where you have to fight your way back out of the building that is now swarming with cops and SWAT. After you've likely used up all the health items in the area and the SWAT are much tougher and better equipped than the butchers you just fought.
In Postal 2, you can pee on things. Peeing on people generally causes them to throw up violently, with some fairly advanced liquid physics for the game's time. In one level, the Dude gets gonorrhea, and his urine becomes green and burns when you pee, which guarantees that people you pee on will throw up in reaction. And it's possible to decapitate someone as they're vomiting, causing it to continue to spew out of their neck stump.
The cats and dogs in S&M gear near the end of Apocalypse Weekend.