To begin, we start with some of the agents- the geisha and the metsuke. Geisha as portrayed in the game and as known in popular culture did not exist until long after the end of the Sengoku era. A good replacement might be kunoichi, but kunoichi didn't JUST seduce-then-assassinate people. They also carried out the same sort of work male ninja did, so they'd have to be just more versatile ninja. Metsuke were completely a creation of the Tokugawa shogunate and thus, given how easily the Tokugawa are eliminated in game, shouldn't really exist. There's nothing explicitly wrong with either role they have for a unit, but it's the skin/flavor they used that's innacurate. I do appreciate monks-as-agents, as a lot of Sengoku daimyo did have monks as friends who would act in their interest- but not really in conversion. It was more in a diplomatic role.
Then you get to the start date of 1545 and the problems that causes:
- At the time, the Uesugi were not known as the Uesugi- they were the Nagao. The Yamanouchi and Ogigayatsu? Those were the two branches of the Uesugi. Nagao Kagetora, later Uesugi Kenshin, would not become adopted into the Uesugi clan and thus make himself the head of it until the early 1560s.
- Similarly, the Tokugawa clan were NOT the Tokugawa at the time. And they wouldn't be until 1568. They were the Matsudaira until then. And it's quite likely Ieyasu's father, who you start as, wouldn't have necessarily changed the main branch clan name to Tokugawa at all.
- Otomo Sorin's father is the leader of the Otomo clan in Shogun 2 at the start... but his father was never Christian. Ever. And he himself didn't convert until 1578. So the Otomo starting off as THE Christian faction is horribly innacurate.
- And the Chosokabe? Nowhere near powerful enough at the time to do the steamroll the other major factions can do. They should have it as hard as the Tokugawa. This one is more of a nitpick, admittedly, though.
- Kenshin, though a devout worshiper of the Buddhist god of defensive warfare and luck with finances, Bishamonten, for his entire life, also wasn't a Buddhist lay clergy at the time, so he would've still been seen in armor rather than his iconic headwrap.
Then there's the whole business about archers being woefully ineffective by themselves when the vast majority of combat deaths in the Sengoku (and most of Japanese history until the introduction of the arquebus) WERE from arrows.
Oh, and the Hattori. God. I hate the Hattori in Shogun 2. The Hattori were retainers of the Tokugawa. Yes, they originated from Iga, but they weren't a major clan in of themselves and only became infamous thanks to Hanzo, who again, served the Tokugawa --in Tokugawa lands, not Iga-- as a samurai landowner as much as a ninja. What they represent, the Iga Republic, was a conglomeration of a bunch of tiny clans whose heads voted democratically on what to do. They also really weren't interested in expansion. They instead hired their services as shinobi out to other, larger clans. So, to have this super minor clan that really doesn't have much to do with the Iga Republic past a certain point represent them and also be one of the most major threats in the game? It's "Ghandi with nukes in Civ" levels of silliness.
Also, I understand the purpose of the Realm Divide- to sort of emulate the problems Nobunaga had after entering Kyoto and asserting his dominance over the Shogunate. However, given the politics of the era, if the Ashikaga clan were flat out attacked with a sizeable army, it wouldn't have made every clan immediately pissed at you. You'd really only have the deputies of the shogunate to answer to, and the sole major deputy left who actually both had power and fronted about being loyal to the Ashikaga was the Uesugi clan. Otherwise, they'd be too, too busy with the rival clans around them to really care. This was an era of social upheaval- and that included the upheaval of caring about the Ashikaga. Sure, a lot might think you're a stinker- there's a reason Matsunaga Hisahide was known as "the villain of the warring states" in Edo era literature. But they wouldn't do anything unless it could benefit them.
This is just from what I can remember, too, mind you. I'm sure I'm forgetting a bunch. It's been a while since I last played it. Good game, but, as a Sengoku history buff, the pledged "accuracy" compared to all the anachronism always kills me inside, especially when you compare it to Nobunaga's Ambition. Like I love silly, fun, purposeful anachronism, like with Sengoku Basara or Samurai Warriors. But it's not that. It's just flat out wrong and presented seriously. It doesn't make it a less fun game, but suffice to say I'm disappointed with it. They could've easily kept the game fun with necessary gamification anachronisms without being so, well, anachronistic in ways which really don't improve things.
It's also important to note that you really didn't have rigid, regimented, standing armies in the era. Sure, you had some trained samurai and people who made their living as warriors. But mostly, you had given landowners gathering up able-bodied men, who usually knew how to fight or fire an arrow given it was a requirement of the era, then answering to the call of more powerful landowners in the area to go to war. However, I understand this makes gamification REALLY REALLY hard, especially in RTS titles which follow more rigid systems of warfare, so I tend to handwave it.
I will note I do appreciate some of the anachronistic things they did as they played up war stories and legends of the era- the DLC with nun warriors, for instance. But it feels like they're supposed to be exceptions rather than the rule... when they
are the rule. Which would be fine if they just embraced the rule. But they aren't, so it's annoying. If that makes sense?