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.
YMMV: Ninja Gaiden
Adaptation Displacement: Somewhat of a subversion. Most of the fans who are aware of the 2-player Beat 'em Up version of the arcade believed it came before the first NES game. In reality, the arcade version was developed simultaneously with the NES version, with the two teams making their own game based on the same basic concept.
Angst? What Angst?: In Ninja Gaiden 3 Once he's freed of the masks control of his mind, Theodore doesn't seem to be fazed at all by all of the horrible things he was forced to do, or the fact that his brother and grandfather were the ones who forced him to do it, OR the fact that his daughter is serving as the core for a giant monster ravaging Tokyo. This is later subverted in his last battle against Ryu as he implies him that he is aware of everything that was going on while he was the Regent of the Mask. He sacrifices himself not only to allow Ryu to free his daughter, but to receive his "atonement" for his crimes as well.
Anti-Climax Boss: Sort-of with the Dark Disciple, who claimed to have the power of the "Devil Incarnate", but gets punched out anyway
He was piss easy in the original game, but Ninja Gaiden Black significantly upped the difficulty by nerfing the Flying Swallow (a diving sword strike that would be a Game Breaker in the original, if it wasn't already Nintendo Hard).
Considering that roughly 70% of the game is spent chasing her down, Elizabét in Ninja Gaiden II isn't much of a challenge. She's arguably easier than Volf.
Until Sigma II rectified it: like with the Dark Disciple, good ol' flying swallow spamming won't work this time!
The Final Boss in Ninja Gaiden 3. Not that the fight isn't visually impressive, but you spend maybe 30% of it fighting fiends it sends at you, another 30% doing QTEs and 40% actually fighting it (the way you fight the Statue of Liberty in Sigma 2 more or less). All in all, it is probably the easiest boss of the game.
Big Lipped Alligator Moment: At the end of Day 5 in Ninja Gaiden 3, you find yourself fighting a suddenly colossal Oobaba (who was supposedly killed by Ayane in Sigma 2) on the way to see Ryu's father in his retreat. This is never explained, has seemingly no connection to the rest of the plot and is never mentioned again. Razor's Edge only briefly mentions that the BS Ninjas are actually working with LOA, although the reason remains vague.
Broken Base: Ninja Gaiden Sigma 2. Some consider it inferior to Ninja Gaiden II because of the lack of gore, lessened difficulty and the removal of puzzles. Some consider it superior thanks to a more balanced gameplay, less cheap AI and the removal or revision of the most tedious passages of the original, as well as having more content. The drastically reduced number of enemies and the introduction of a semi-automatic aim for the bow can be seen a good or a bad thing depending on who you ask.
Contested Sequel: Yosuke Hayashi's drastically different vision for Ninja Gaiden 3 let many fans skeptical to say the least. Some fans think it is still a fun action game in its own right, if not on par with the first two games. Others prefer to pretend it never existed. Interestingly, Hayashi was already involved in anotherContested Sequel...
Crowning Music of Awesome: The Ancient Ship of Doom has one in form of the theme from Stage 1-1. It's awesome as it's catchy.
Demonic Spiders: The ghost piranhas (WHAT?!) infesting the labyrinth in Zarkhan for Ninja Gaiden (Xbox). Their pack tendencies, respawning capabilities and sheer, unimaginable tenacity make one question the existence of a just and loving God and ask why the game's designers hate the player so damn much. In fact, just about all of the enemies drop into this territory at higher difficulties.
Originally, the ghost piranhas were just decorative, until Itagaki found out about them and told the team to make them enemies.
Their difficulty may be toned down in the sequel, but there is one chapter where you have to deal with them alongside the Water Dragon. Painfully worse in II but noticeably easier in Sigma 2.
In the first game, especially at the highest difficulties, a good portion of the non-human mooks are this, really. The black "laser eye" fiends or the cat fiends are just hellish to fight in groups.
Ninja Gaiden II has a literal kind with Black Spider Ninja Rasetsu, as the boss on the first level. He and his other derivatives turn into common enemies later on.
The birds in the NES games. Oh God, the birds.
You liked the Goddamn Bats in the first Xbox game? In Ninja Gaiden II, meet the giant bats! They are thrice as big, make thrice as much damage, are thrice as tough and are still unblockable. More often than not you will take damage while trying to kill them.
In the same NGII, the infamous Incendiary Kunai Ninjas are usually this when you fight them in large groups. Take a guess why by looking at their name. Strangely, in Sigma 2 they are also dreaded enemies, but for a different reason: they use their explosives less often but are much tougher and much more competent at close combat instead. Especially in higher difficulties, where their claw attacks deal huge damage.
8.8: IGN's 3.0 of Ninja Gaiden 3. It gained quite the backlash already. The Updated RereleaseRazor's Edge, however, got a much more decent 7.6.
Ensemble Darkhorse: Robert T. Sturgeon in The Dark Sword of Chaos. A Mysterious Informant/Protector with an agenda of his own, Cool Shades, able to take down demonic horrors with a single gunshot, who turns out to be a top United States Army operative and such an extremely loyal ally to Ryu that he makes a Last Stand to guard his back in the very bowels of Hell? This is especially notable considering how well Ryu gets along with covert government agencies...
Momiji. She has garnered enough popularity to appear (and possibly be a playable character) in the recently-announced new Dead or Alive 5.
Game Breaker: The Unlabo(u)red Flawlessness in Ninja Gaiden, when used by a player skilled enough to stay alive at 15% health, can cut enemies down with shocking speed (most of them at any rate). Then again, given the strict health requirement and the game's difficulty, this isn't as severe as the others listed.
The Izuna Drop in all the games is fairly easy to execute and will instantly kill any human-sized mook. In Ninja Gaiden, enemies often block and you can only do it with "katana-like" weapons so its use is restricted. However, the sequel allows its use with almost any weapon, and enemies don't guard at all. Sigma 2 nerfed it slightly by making some mooks (almost all of them on Master Ninja difficulty) resilient enough to survive it.
Ultimate Techniques are a similar case: in the first game, without absorbing essence to speed it up, it takes 4 seconds to charge a full-powered UT and their range of effect is limited. In Ninja Gaiden II, it takes only 2 seconds, with some weapons' UTs being glaringly over-effective on large groups of small mooks.
You can execute a normal jump attack by holding down while you attack.
The Eclipse Scythe in 3, despite its slowness, can become this if used properly. With the sword or the claws, you can directly repeat a successful steel-on-bone attack on a nearby enemy; with the scythe, "nearby enemy" means "any enemy within a 5 meter radius". As long as you don't screw up the initial steel-on-bone, you can take down entire waves almost effortlessly.
As of Razor's Edge, this scythe has taken this trope almost completely, with only a few drawbacks (notably the limit on the number of successive SoB).
Goddamned Bats: Actual bats for the modern games. The critters do annoying damage, and come in large packs. Explosive variants start showing up from Black onwards. Almost all the enemies start as this and become Demonic Spiders on higher difficulties.
Bats are also regular enemies in the NES games, and they're in all respects similar to Castlevania bats.
Goddamned birds in the NES trilogy! The bats at least fly in a predictable pattern and usually aren't too hard to simply avoid, but the birds actively home in on Ryu. And they're almost always by ledges and pits.
The "jellyfish" in the amazon level for Ninja Gaiden II. Sure, they don't move and are easy to eliminate, but they get in the way...and they just. Never. STOP. SPAWNING. Of course, you can try to swim trough them... at your own risk.
Dogs, blue bugs and homunculi often act as this in Razor's Edge.
Goddamned Boss: The infamous giant worm boss in the Amazonia level of Ninja Gaiden II. It's not even difficult, simply horribly ill-designed: 90% of the time you'll not see it, even when you're hitting it. It was so bad that Sigma II didn't even try to make it better: they just mercifully removed it from the level, along with the entire "green tunnel" section. You won't even notice it.
The two "armadillo" bosses in the underworld level in Ninja Gaiden II. You don't know the meaning of Camera Screw until you've gone through this fight. Like the giant worm, Sigma II removed it, replacing it with a fight against Marbus.
Good Bad Bug: In Razor's Edge, Kasumi has a version of the Cicada Surge called "Sakura Madoi", which allows her to evade not only melee attacks like Ryu, but also bullets and missiles. Which means you can use it to teleport into areas that are normally inaccessible, and in extreme cases, even out of the map. It was sadly fixed in the PS 360 version though.
Even hilarious in the case of the recently-announced Yaiba: Ninja Gaiden Z, which is a sidestory for the modern series.
I Knew It: Due to the breadth of shared traits between Irene Lew from the NES trilogy and Sonia of NGII, more than a few fans theorized that Sonia was a modern re-imagining of Irene and that they were the same person (Sonia's bio even hints that her name is an alias). Come Dead or Alive: Dimensions, it turns out that they were right.
It's Easy, so It Sucks: Ninja Gaiden 3 is a far cry from its punishing predecessors. No wonder it's being critically savaged!
The Razor's Edge edition ratchets the difficulty back up for normal, but does include an easier mode that can be selected at any time.
Narm: The Worlds Of Power book is filled with this, starting with the groaner on the first page, "Dedicated to the ninja in everyone's dad."
The "don't kill me mate" scene at the very beginning of Ninja Gaiden 3 is so overdone that for many it ends up being hilarious instead of a Player Punch. To the point it was removed in Razor's Edge.
Nightmare Fuel: About the only thing anybody knows about the original arcade machine is the circular saw from the continue screen.
Only The Creator Does It Right: What certain fans think about the modern trilogy and one of the reasons there's so much bashing on Hayashi's games (both Sigmas and Ninja Gaiden 3). Any title not directed by Itagaki can only be a pale imitation. It doesn't help that before leaving Tecmo, Itagaki specifically said he didn't like Sigma, that Ninja Gaiden II was the definitive version of the game and that he was the only one legitimate enough to continue the series.
Player Punch: Ninja Gaiden 3 goes to great length to make you feel the pain of the enemies you kill, be it the brutal Steel-on-Bone mechanic or the moaning of enemies if you don't finish them off.
Crawling and bleeding mook: I don't wanna die... I don't wanna die!
Polished Port: Razor's Edge, and how. Apart from the addition of several weapons, upgrades, collectible items and a playable Ayane, nearly every single aspect of NG3's gameplay has been improved, from combo speed to responsiveness, to enemy AI, to the use of the ki bar and the steel-on-bone mechanic, making the game much more technical overall. The PS 360 version also corrects the frame-rate drops.
Porting Disaster: Of sorts. The Greater Fiends in the DLC missions of Ninja Gaiden 3 were merely ported from their respective games (Doku and Alma from Sigma, Alexei, Volf, Zedonius, Elizebet and Marbus from Sigma II). Their models were not polished enough to be compatible with the game's engine, making them really buggy and glitchy to deal with, with Marbus being the worst offender. Same thing goes for Genshin (both in his human and Fiend forms). Razor's Edge fixes them for the most port, although some glitch remains, notable for Elizebet.
Replacement Scrappy: Although not a big fan favourite to begin with, it's amazing how much Sonia in Ninja Gaiden II can make you miss Rachel. Depending on how you see it, may or may not be rectified with Sigma II.
Every woman in the modern trilogy is this to old school fans who still see Irene as Ryu's One True Love.
Which is all the more ironic in the case of Sonia, considering that she and Irene are one in the same.
Scrappy Mechanic: The save system in the first X-Box game makes it so that if you die, you have to restart at the last save point, no exception. Meaning if you die against a boss, you have to redo the section between the save point and the boss. And if you die at the beginning of the following chapter without having saved, you have to redo the boss.
The steel-on-bone mechanic in Ninja Gaiden 3, not so much for the mechanic itself but because it activates pretty much randomly and interrupts combos. It has been reworked in Razor's Edge, where this attack is now used to counter enemy grabs.
Seinfeld Is Unfunny: Someone watching the plots of the NES series today will find them narmy and a bit overdone with their "three twists per second", but at the time they were a big leap forward for videogame storytelling.
That One Attack: Zedonius' flame wall in Ninja Gaiden II is unblockable and undodgeable. Even some moves with invulnerability frames don't protect you! The only thing you can do against it is use a ninpo, but if you're out of it, pray he doesn't use it.
Actually, it is dodgeable. You have to stay away from him when he is about to attack you with it.
That One Boss: Just about every single one of them, especially in the modern games.
Murai in Ninja Gaiden deserves a special mention for being not only the first boss of the game, but being so goddamn hard to start with.
That One Level: The infamous 6-2 in the first NES game. 6-1 and 6-3 are both extremely difficult as well, but 6-2 takes the cake for cheap deaths and one spot where you seemingly have to exploit a flaw in the programming to get past. If you die even once on any of the three final bosses, you're forced to redo the entire stage at 6-1 again.
The "Path of Zarkhan" chapter in Ninja Gaiden. Not that it's particularly harder than previous chapters but you spend most of the level swimming back and forth to solve a puzzle, and after that you must go through a very long and boring swimming sequence through areas previously visited but now submerged. Sigma removed that puzzle and made the level more straightforward, but you still have to swim a lot.
Unfortunate Implications: In Sigma II, you play a Japanese man who literally fights the Statue of Liberty. Granted, you were fighting a statue of Buddha two stages prior (presumably if the series ever goes to Rio de Janeiro, we'll fight Jesus).