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.
Badass Decay: Yoshimoto, when compared to his historical self. Real-life Imagawa Yoshimoto is actually pretty menacing, cunning and effective as a daimyo, rivaling even Shingen and Kenshin. But because he's the guy beaten brutally through sheer luck by Nobunaga on the latter's first big battle (and then kickstarted the Three Unifier's era of the Sengoku period), he becomes a more or less incompetent buffoon, the equivalent of Zhang Jiao in the game. In 4, Koei tries to mitigate this by showing that Yoshimoto has a dark, serious side that rarely comes out and shows how terrifying and dark he is as a successful daimyo.
Crazy Awesome: Hojo Ujiyasu. He'd have to be to pull off some of the insane stuff he does.
Crowning Music of Awesome: Yukimura's last stage, Siege of the Osaka Castle in SW3. Fight until Hideyori is killed by Hattori Hanzou and then listen.
Mouri Motonari. He wasn't officially revealed until one day before the release, didn't get mixed in the whole Ho Yay/Foe Yay stuff either and he is also nothing close to a Musou bishounen. Yet fan artists just love him.
In a popularity poll coinciding with Samurai Warriors 3: Empires Sakon Shima wound up being the fourth most popular character behind only Mitsunari Ishida (one of the series' most important characters), Yukimura Sanada (the poster boy), and Gracia (who probably also counts as a darkhorse).
Spears in Katana can critical against nearly every enemy in the game, 1-hit-killing all but a select few of them without any stat raising.
In 2 Empires, we have the wheel formation. Not only does it give you the normal speed and morale boost if it's the better formation, but it also Doubles Your Attack And Defense, effectively turning almost any battle into a curbstompbattle if your enemy doesn't have anything to counter it (which is a 1 in 3 chance for every formation they still have).
Also the five scrolls in the first game. If you equip all five, your elemental attacks becomes One-Hit Kill attacks that severely damages officers. On a similar note the "Demon" element from the second game, which was changed in Xtreme Legends.
Matzukaze, Keiji's horse, will make you One-Hit Kill anything that your ride over if going at top speed.
In SW1, Okuni's charge attacks (notably charge 2) possess ridiculous amounts of power.
In the second installment, Musashi is hilariously broken for three reasons. Firstly, he has the personal skill Reversal. Whereas other characters can be stunlocked if struck several times in succession, Musashi can just hit the charge button and interrupt the combo to send his attackers-turned-victims flying. Secondly, he has an ability that stuns enemies and gives him free Musou, which means that he has unlimited Limit Breaks at his beck and call. Also, did we mention that he has one of the most devastating Musou attacks in the game?
Tadakatsu Honda is known as this series' Lu Bu, but the Interlude compares him to Zhange Fei, however he is mildly faster than both (probably having above average speed between SW characters) and all his attacks causes absurdly high damage! Not only that but his two Specials allows him to stun enemies and regain 1/2 of musou and to cause contact damage on enemies. His Musou can clean a room in SECONDS.
Germans Love David Hasselhoff: When Koshosho was revealed, the Japanese were really annoyed at her design and her list of manipulated men includes 'Sengoku Musou fans', that were pissed that she made it in with her outrageous design when other more popular choices like Miyoshi Choukei or even Motochika's wife Nana didn't make the cut. Western-wise, she's considered to be so utterly fabulous that some are considering to make her their favorites.
Spears in cannons that fire laser beams, ancient Nipponese shoop-da-woops from Ofuda scrolls, ninja with arms straight out of Gumby... just turn your brain off before playing. For your own sake.
The plate mail armor may seem like this but it is in fact Truth in Television. Armor in the late 16th century Japan was influenced by Western plate armors after things like muskets start to show up. Nobunaga himself was historically a foreign artifact fanatic and had worn quite a few so called "Nanban" style armors in occasions.
No Export for You: Samurai Warriors 3 XL/Z and Chronicles 2nd did not have an international release.
Replacement Scrappy: Despite having her own fanbase, Nene has earned the ire of some fans for replacing Kunoichi (who was removed) in SW2. The fact that they have similar movesets (especially as Nene was never a ninja in real life) doesn't help her case. While Kunoichi does return in SW3, the fact that her role is more centered towards Yukimura (and, to a degree, Kaihime) while Nene is shown to do more ninja activities (including sharing a rivalry/relationship with Hanzo) doesn't put an end to the "Nene shouldn't be a ninja" debates. Kunoichi lampshades this by calling Nene her "Spiritual Successor" in a Warriors Orochi 2 Dream stage.
Hisahide Matsunaga is ill received for his ridiculously over the top character design (even by SW standards), general pretentiousness, the undue importance put on his presence in the Oda camp (and for some reason suddenly took credits to Hideyoshi's accomplishment in Kanegasaki in the Oda Legend chapter, though it's much to Hisahide's chagrin), and soaking up what some feel to be a disproportionate amount of screen-time.
In Katana, the second Saika mission with Ina. You have to defeat 15 enemies [including transport units] in 4 minutes (slightly extendable via the Magatama item). The ninjas are invincible when they prepare to teleport out of your sight. Curiously enough, the game actively avoids Luck-Based Mission here and instead hits Guide Dang It. How? Any specific enemy appears ONLY when you enter a certain intersection from a certain direction. Once this is realized, The level becomes more a case of plotting out your exact route through the map so as to get the most amount of ninjas to appear in the shortest amount of time.
Sakon Shima's Dream is a pain even on Easy. Why does it count as if Ieyasu escaped if only one of his doubles (And you KNOW it is a double) does?! Added Hideyoshi, Mitsuhide and Tadakatsu have this strange habit of getting to your main camp.
They Changed It, Now It Sucks: The whole Free Mode Only Characters debacle in SW3, in which the story campaigns of several returning characters were left out.
KOEI ignored the reason Gracia's famous in the first place in favor of an original story with her and Magoichi in her first appearance. The Other Wiki has a good article on her actual history. They pay a little more attention to her history in SW3:XL, though they still skip on the reason she's famous. Chances are it's to avoid any religious controversy.
Unpopular Popular Character - Katsuie's relationship with Oichi (historically, it's rumored that they were engaged to be married before Nobunaga decided that a political alliance with Nagamasa was more profitable) is severely downplayed to the point of it being nearly non-existant in favor of her relationship with Nagamasa. However, if fighting the Battle of Shizugatake (Katsuie vs. Hideyoshi to "succeed" Nobunaga) she is on Katsuie's side.
It's easy to mistake Mori Ranmaru for a girl and it is somewhat of a a running gag in-universe. He uses female motion sets, is voiced by a woman in the Japanese games (and in English as well, starting from the second), and is frequently used to Drop A Bridget OnChivalrous Pervert Saika Magoichi and other such characters.
The Woobie: Many characters could be considered this depending on what story you are playing through. Ranmaru in SW1 is a good example; everyone he cares about is trying to kill each other.
Nohime: " Ranmaru... did you ever know.. happiness?"
Woolseyism: In the Japanese version, defeating an enemy general makes the character exclaim "Tekishou, uchitottari!" AKA "Enemy Officer Defeated!". Dynasty Warriors mostly go with direct translation, but Samurai Warriors translates with variations to the point that by the 2nd game, NOBODY ever said exactly "Enemy Officer Defeated!" when they defeat a general. In the 3rd game, each character has two variable "Enemy officer defeated" lines with the first one being the standard "Tekishou uchitottari" and the second one tailored to the character's personality.
WTH, Casting Agency?: Your mileage may vary, as it depends on which version you played first; it certainly doesn't help that the roster gets cleaned out with every numeral. Most seem to agree that Keiji's VA in SW2 was a definite downgrade from his well-loved one in SW1.