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.
Sue as well for taunting a gigantic frenzied Mimiga and then promptly getting pummeled into submission. But much less so.
Ass Pull: The relationship between the third to last boss and the last boss: killing the Load-Bearing Boss causes the island to fall, but killing the next boss causes the island to stop falling. Sloppily handwaved with something vague about "negative energy".
Awesome Bosses: The last five bosses are the pinnacle of the game. And the boss preceding them is a symbolic one.
Bizarro Episode: The Outer Wall is by far the weirdest place in the game. The gravity is odd, treating the left side of the screen as 'down' for everything except you (though this could be justified if the wind is strong enough — this is the outside of a Floating Continent, after all). The enemies don't seem bizarre at first, but then you encounter the giant cat ghosts that shoot yarn balls with eyes at you. And living at the bottom is a group of people that are five inches high.
Breather Level: The Plantation is rather easy compared to Outer Wall and what's to come. Most of the enemies in this area are rather weak or easily avoidable, save points are plentiful and there are no bosses.
The Waterway, right after the Labyrinth, which has much weaker enemies and the water currents that literally complete most of the level for you.
Broken Base: The developer's forums for the WiiWare version were ablaze with people complaining about the music, the graphics, the gameplay, the dialogue... it's descended to the point where "devoted fans" were refusing to buy the game when it comes out because it was delayed.
Complete Monster: The Doctor was initially with the research expedition to The Island, but his true purpose was to seek the Demon Crown and wield its power himself. He also kidnaps and performs Psycho Serum experiments on the local tribe of Mimigas in the hopes of transforming them into mindless monsters for his army and is working on a project to do the same thing to humans. He's killed several Mimigas and many baby dragons. The dragons left alive he turned into his undead servants.
Demonic Spiders: The armored Gaudis in Labyrinth M. They throw knives at you which do loads of damage, and unlike the purple projectiles from the flying Gaudis, they can't be shot down.
The green birds and Butes listed as Goddamned Bats below become this in Hard Mode.
Ear Worm: Good luck getting Balrog's Leitmotif out of your head. The aforementioned Main Theme and Running Hell also qualify.
And the actual bats in the game, which can swarm around you if you don't kill them while sleeping, and are particularly obnoxious when summon spammed by bosses.
Goddamned Boss: The Core, with periods of invulnerability and ability to flood the area, which slows you down and may drown you. Also, the boss area is quite far from the previous restoration point even if you aren't going for the Golden Ending.
Good Bad Bugs: Playing in Holiday Mode in the Wii version somehow turns Curly's sprite into Quote's. Not only is the now-male "Curly" referred to as "she" and "her", you still meet Quote in the Sand Zone. For the rest of the game two copies of the main character are running around the island.◊ And Curly's panties are still referred to as "Your Panties". Yeah.
Cave Story 3D has a huge glitch where the game saves flags between save files when you quit the game with the inventory open. This can be used to return from the Point of No Return, get huge amounts of HP, and numerous other wacky things, including getting a Dummied Out item that Nicalis, surprisingly enough, ported into the remake.
Quiet, the tune that plays in Mimiga Village after you come out of the Waterway. *shudder*
It's even worse in Santa's House, Chako's House, and the Sand Zone Residence.
Your PC has a hardware synth card like a SoundBlaster X-Fi? Switch your PC to it's onboard audio instead before playing- the game music is an eardrum-splitting wreck if played through the X-Fi for some strange reason.
Most Annoying Sound: The sound of experience points bouncing on the ground is barely noticeable in the original PC version, but drowns out everything else on the WiiWare port. This has been fixed with the recently released update.
Paranoia Fuel: One of earliest doors you'll have to enter is literally a monster. However, this monster never appears ever again after this initial trap.
This seems to be The Doctor's job throughout the game, since he sure as hell doesn't spend any time healing anyone. If he appears on screen, he's either trying to punch your character or trying to punch you.
"Curly's life functions have ceased." Five little words to let you know that you dun goofed.
Polished Port: The number of ports of the game are comparable to the number of ports of Lunar: The Silver Star, and each capitalizes on the last. The WiiWare port has redone sprites, the ability to play as Curly, and the European version gets an additional soundtracknote Later the NA version would have its debatable soundtrack replaced with the European soundtrack. Cave Story + has all this and the Wind Fortress, somehow harder than the Sacred Grounds. 3D has polygonal models, and Cave Story +'s eShop release boasts everything + does but the graphics, and to compensate it's in stunning 3D.
Monster X is a mine car that drives from one side of the room to the other, forcing you to climb on it to avoid being crushed, and can only be damaged when it stops to unleash a torrent of bullets or homing missiles. While not the toughest boss in the game by any standards, it's far tougher than anything that came before it, and the sheer amount of on-screen objects can be overwhelming even to a player who has played the game before.
The Core has five mini-cores that together create an impressive volume of fire, and severely hampers the player's mobility by frequently flooding the room. It Turns Red by adding a current to the water and starting to use an attack which takes off 20 HP (of a maximum attainable 41 at that point).
The Sand Zone. The Egg Corridor prepared you, Grasstown/Bushlands is where the game really starts, the Sand Zone is where the Nintendo Hard and Guide Dang It nature of the game starts shining, featuring the first opportunity to miss out on one of the two Infinity Plus One Guns, enemies that gang up on you and can cause notable damage together, and a Fetch Quest that forces you to go through the area where the most enemies gang up on you at least five times and forces you to go through that area and the area after it twice. Not to mention Omega and Frenzied/Rabid Toroko, the first two Wake Up Call Bosses...
Labyrinth for enemies that gang up on you a lot, a lot of rooms, and Monster X and The Core, the first two That One Bosses.
Last Cave (Hidden) introduces a mechanic not seen anywhere else in the game up to this point: The game resets all of your weapon levels! While this means nothing if you're using the Nemesis, which is most powerful at level 1, or the Spur, which is a Charged Attack weapon, your other weapons will need some time to build back up to level 3. Additionally, there's a sequence at the end where you have to run past a bunch of Presses that One-Hit Kill you if they smash you into the floor, and perfect timing of Booster 2.0 is needed to get past the small water pits in the floor.
They Changed It, Now It Sucks: Balrog's quirky Catch Phrase ("Huzzah!") became "Oh Yeaahhh!" for the WiiWare release. Fans were not pleased. Also, some of the music sounded worse, although in this case the consensus was nearly unanimous, with the real debate being how big a problem it was. Nicalis heard the complaints, and eventually released an update that fixed the sound, music, and a few grammar/spelling quirks.
What Do You Mean, It's Not for Kids?: The game is known for its accessible and engaging gameplay and cutesy visuals. It also features slavery and war themes, four nightmarish final bosses (The Doctor, who loses control and mutates, then him possessing the Core, Sue, and Misery, then the Heavy Press which attacks out of nowhere and is a Kaizo Trap if you don't realize what it is quickly enough, then finally Ballos, who has a horrific backstory and red, tortured faces in his head), and most of the cast dying before your eyes at regular intervals.
Woolseyism: Many consider the original fan translation far superior to the more Wonder Bread official localization that came years later. While the official translation clearly borrowed from the fan version used for years, it removed scores of little nuances and phrasings that were more dynamic and made each character seem more identifiable in how they came across. Of course, in many cases, the preference is as simple as changing Balrog's iconic "Huzzah!" to the "Oh yeeeaaah!" Kool-Aid Man reference.