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.
Anti-Climax Boss: The True Evil Pig in the first game. Unlike the other Evil Pigs, he doesn't even have any real attacks; his sole power is to freeze you in placenote which actually provides a neat bit of Foreshadowing for the sequel which, while making him harder to hit, means you can't really die in his fight unless you're just really, really bad and keep running into himlike an idiot. The sequel does a much better job with its final boss.
Awesome Music: Both games have some good music, such as the boss fight theme in both games.
Hilariously, all of the non-story-related NPCs in the second game were voiced by the same person.
Nightmare Fuel: Don't eat those mushrooms. Everyone will laugh. Or cry.
The Ghost Pig in the sequel is quite creepy compared to the others who are at least goofy.
The sequel's endgame sequence where the final Evil Pig freezes time. Everything's in black and white, the world is pitch black outside of your immediate surroundings, and everyone else has just up and vanished. To top it all off, it's all accompanied by thiswonderful"music"!
The Orange Pig in the jungle is also pretty bad due the fight being in a tall and vertical room and the bag was rotating at the top of a series of tiny platforms.
The evil Earth Pig in the second game may also count.
That One Level: The cursed version of Phoenix Mountain. Especially, the second section of the mountain where you need to jump across a bottomless pit on three extremely narrow platforms spaced really far apart without messing up and falling into the bottomless pit. It is also not made any easier by the fact that the wind makes it impossible to time your jumps carefully.
It gets even worse when you're inside the mountain and have to carefully jump onto a series of small platforms to avoid the pits of fire on the bottom.
That One Sidequest: The Race mini-game in the first game, and the Trolley one in the second.
The race in the first game was actually pretty simple when you learned the trick, avoid jumping as much as possible unless there's a direct obstacle, and stay on the ground as long as you can so you can stay at top speed which would allow you to finish the race quickly.
Two words from the first game that make everyone flinch, "Seven Friends". This is one of the last and mandatory quests in the game. The required friends are in random places all over the world, and when you find the first six, you might go crazy looking for the last friend only to find out that it's actually Baron.
From the second game, ladies and gentlemen, let me introduce you to the Secret Towers. Each of which requires a pair of Guide Dang It sidequests to even get the key to open. Then you have to find the door to each (also a Guide Dang It, as the game gives no hint as to where the doors are, and they're invisible). Oh, and there are three of them. Most players give up long before discovering the Platform Hell within.
Also from the second game, we have the "Precious Ring/Miner's Ring" you have to drop in a specific spot JUST to complete it, but the spot is so hard to get into that it's just being mean.