The stance toward Nuclear Gandhi. Originally a (rumored) coding error, the meme quickly picked up speed during development of IV and became actual gameplay mechanics by V. Some consider it a funny Running Joke and a series mainstay. Some are annoyed by it and consider it a Dead Horse Trope, others find it boring on the merit of being stuck with Gandhi leading India simply due to a one-off joke and also facing extremely predictable AI in each game.
Civilization III:
The game introduced many concepts that from modern perspective are essential bits of the whole series, but on their introduction, were highly divisive. That list includes things like strategic resources, culture and cultural borders or the clear distinction between workers and settlers. People either couldn't get more of those changes or were infuriated by how poorly implemented they were. Most prominent issue was the role of strategic resources, due to the way how they were spawned on the map and how much the game could be decided by access to them - with both sides arguing either more in-depth strategies needed rather than just spamming units or the fact one could get stuck for good without access to proper resources.
In vanilla game, unit roster was much tighter and various units had clear expiration date, without ability to upgrade them. And a whole lot of units required access to strategic resources, which meant once the access was cut, one could end up with situation where constructing new military units was no longer feasible, as everything older was no longer possible to build and contemporary units lacked specific resource. This by itself was a minor point of argument between players, but things accelerated with expansions, especially Conquests. Countless units that not only don't require any resources at all, but are also cheaper and often come with better stats were introduced, along with ability to carry them over eras, virtually making it impossible to lose ability to produce units, along with making various "vanilla" units utterly redundant. People supporting the change obviously argue it's no fun having obsolete units that can only be disbanded and being unable to produce any unit at all due to RNG. People against this argue that this allows a whole lot of gamey tactics, removes any kind of strategic thinking from the game and reverts the game to the state from II, cutting out a lot of progression done in vanilla III.
Civilization IV:
The game removed the ability to plant forests. While III already cut down on the number of terraforming options from II and Alpha Centauri, IV removed ability to get forests easily. You could cut them down at any moment, but there was no way to plant them back - they could only (re)grow on their own, which was a random event and could only happen in specific climate. Some say it's insignificant in the grand scale of things and there are more productive tiles than forests. Others argue that Lumbermills are one of the better tile improvements out there and inability to plant forests can really hurt your production rates in various locations that would be perfect to settle, if only they could grant small boost to hammers. Still others say that being unable to replant forests is a Necessary Drawback for the huge early production boost that clear-cutting gives you, and being able to replant forests would make it too easy to have your cake and eat it too.
One of the minor goals of Caveman2Cosmos, an extensive total overhaul mod, was finding a satisfying solution. The end result is a tree nursery, which allows to plant and re-plant forests. But it takes dozens of turns for the nursery to grow into an actual forest, similar how hamlets turn into villages and then towns overtime in vanilla game.
Civics. While parts I to III had direct government forms of your civilization, IV instead abandoned the concept and allowed to mix and match various features, similar to Alpha Centauri's social engineering. Supporters praise it for adding much needed variety, rather than bee-lining for specific government ASAP and sticking to it without a second thought for the rest of the game. Detractors complain that you still want to bee-line for specific civs that are flat-out better than others and the choice, unlike in SMAC, is pretty insignificant.
Mods tend to greatly expand on civics variety, effect and balance, which leads to agreement that the mechanics itself was fine, but it was the lackluster choice in the vanilla game that undermined it.
Removal of difference between Attack and Defense rating for units, merging them into uniform Power. While some players argued this helps AI with handling units and prevents situations when defenders are in the frontlines or cities are inadequately protected, detractors complained this removes strategic thinking from players side of things, as all you need to do is just build highest rated unit.
Both expansions greatly helped to close the divide, as they introduced additional traits the units can gain on promotion, along with granting certain units traits upon construction, thus making the system both nuanced and easy for AI to handle.
The addition of the "Native American Empire", represented by the Lakota leader Sitting Bull, caused controversy within the player base. While some players appreciated the representation, other complained that the Native Americans were never a unified political group nor engaged in empire building, and the generic grouping failed to represent their vast cultural diversity. They argued that this would be akin to grouping every European civilization under the umbrella term "Europeans".
Civilization V:
When it was announced that V will have Panzer General style combat, will only allow one combat unit per tile, will be released with Steam, that there will be DLC, and that you will have to pay extra to play the Babylonian civilization. Cue Flame War. It bears noting that there is actually a "rant thread" on the Civfanatics forums that was created by the moderation staff specifically to keep the massive firestorm of complaints from cluttering up the rest of the forums and to keep said complaints at least somewhat civil. On the flipside, there were players who welcomed the "one combat unit per tile" rule, citing the massive 'unit stacks of doom' as a Scrappy Mechanic that bogged down the combat of previous games and required next to no strategy.
Gods and Kings continues the tradition, generally making people who liked the game like it more and people who hated the game hate it more, "Religion and espionage were already in IV", "They're totally different here", "that's a bad thing, IV had it right", etc.
The announcement that Brave New World will have the XCOM Squad unit. Some feel it's an unnecessary crossover in a history-based game, others are fine with the idea and point to the Giant Death Robot that has existed since vanilla V.
The inclusion of Venice and its unique role has broken the base in many places. Some dislike it for being another European civilization when the continent is already heavily represented, others are fine with more European civs but would rather have seen a unified Italy and/or feel that Venice has had too little impact on world history, and even some who like the idea of a Venetian civilization aren't fond of its unique ability that prevents it from founding cities, instead having to rely on a unique unit to puppet city states.
Civilization VI:
Upon the announcement many have complained about the new art direction, which has been criticized as too cartoonish for a game as serious as Civilization. Others have welcomed the new style, noting how much easier it is to distinguish objects on the map. And a third group doesn't care how it looks either way as long as the game isn't as horribly optimized as V was.
The District system, more or less the defining new game mechanic in VI, has been both praised for adding endless amounts of complexity and customization to the game, and criticized for being too game-defining, obtuse and requiring too much micromanagement and planning ahead of time to be wielded effectively. As a result, the mere existence of the District system caused some players to abandon VI for older games instead, while others have gone on record to say that they won't even bother playing any sequels that don't also have a District system.
The civilizations and leaders featured in VI have been controversial for three main reasons:
First, concern that Firaxis has been Eurocentric in its choice of civilizations, as the base game has a high density of European leaders with more civs from other parts of the world locked behind DLC.The debate tends to flare up anytime a new civ from Europe is introduced, as many feel that the non-European civs that have been introduced aren't numerous enough. This is also a bother to players who enjoy games on a true-start-location map, as Europe gets crowded very easily while places like Africa and South America do not.
Second, how many of the new civilization leaders are women, and whether Firaxis is picking leaders to be gender-inclusive instead of finding "more qualified" male leaders with greater accomplishments. This topic in particular tends to result in a lot of debates, ranging from genuine historical analysis and discussions of qualifications to accusations of sexism and ignorance about the role women have played in history.
Third, disputes over which civs are being included from a stance of historical importance, with the inclusion of nations like Canada and Nubia before civs like the Maya and Ethiopia. Of course, this provokes debate due to “importance” often being relative. This ties in with some civs being seen as too narrow. For example, many players considered it a strange choice to separate Greece and Macedonia into two different civilizations, as Macedonia was a Hellenistic power and, in fact, Alexander the Great has been the Greek leader in almost every Civ game prior. Other controversies include using Gaul and Scotland instead of Celts and Maori instead of Polynesians. Many feel these more specific civs reduce representation in the game. For example, the Irish were represented under the “Celts” in previous games (particularly V), but are reduced to a city-state in VI. Other players argue that these broader civs would be akin to clumping Russians, Poles, and Ukrainians together and calling them “Slavs”.
For specific civilizations, we have:
Catherine de' Medici. Aside from being ethnically Italian (rather than French), many people are upset by the selection as most of her ruling of France was done behind the scenes; Catherine never directly controlled the French throne. In addition, Catherine received the spot over many popular choices or previous leaders such as Napoleon (who was also Italian, though this is overlooked), Louis XIV, or Charles de Gaulle. Supporters of the decision are happy to see a fresh face ruling the civ, particularly one with such an interesting involvement in history (she was essentially a real life CerseiLannister, albeit a far more competent one). In addition, her role as The Spymaster and the presence of her Flying Squadron (in real life, ladies-in-waiting who had sex with nobles in exchange for secret information to send to Catherine to aid her in her machinations), are seen by many as a compelling and unique bonus that has yet to be seen in Civ VI.
Gandhi is obviously a series mainstay, but many players would have preferred to see a new leader to represent India, mostly because despite being the "founder" of modern India, he was never actually head of state. Some feel this to be a snub to the variety of intelligent, resourceful, capable, competent rulers to select from India's history. Then Chandragupta Maurya was announced as an alternative leader...
Cleopatra. While she is arguably the most famous Egyptian ruler, this is due more to her compelling personality and biography and romantic affairs with Julius Caesar and Marc Antony (immortalized in both history and in Shakespeare) than her being a celebrated leader; after all, her reign ultimately ended with Egypt losing its war, and subsequently its sovereignty, against Rome. In addition, like Catherine mentioned abovenote and coincidentally the other Catherine, for that matter, her Greek heritage being foreign to her own civilization is a sticking point for some fans. However, Cleo does have a fair amount of support for her inclusion, in no small part due to said fascinating personality meaning that she'll likely make for a far more interesting opponent. In addition, her Leader Agenda seems to be following history by making her suicidally aggressive (Cleopatra hates weak civs and city-states, and will slaughter each and every one of them to prove it, often through surprise attacks. This directly conflicts with agendas of rulers such as Teddy Roosevelt, Frederick Barbarossa, or Hojo Tokimune, all of whom have very strong militaries.)
Similar to Maria I in V is Kristina. A good portion of the fanbase (especially from Sweden) was in uproar over her inclusion, as she is mostly remembered in her country as a traitor who brought the country to political and financial ruin following the death of her father and abdicated the throne just to convert to Catholicism, and who was only included to increase female representation. On the other hand, some have argued that her role as a patron of the arts and a promoter of religious freedom, both before and after her abdication would warrant her inclusion, and that she was a progressive individual for her time.
Queen Seondeok of Korea, in additional to receiving criticism for reasons similar to Kristina, has also received criticism because, actual quality of her reign aside, she never actually ruled a unified Korea: Rather, she was the queen of Silla, one of three kingdoms that would later become Korea. Others, however, argue that Seondeok's situation is no different than, say, Frederick the Great's (a series mainstay who ruled over Prussia, but never a unified Germany), or Oda Nobunaga (Who died before technically unifying all of Japan), and that the point is therefore moot, plus Seondeok represents an interesting part of Korea's history that deserves to be represented in some capacity.
Ludwig II, historically known as The Mad King (though his insanity has been called into question by more recent historians) is mostly remembered for his prioritizing architectural and art projects at the expense of Bavaria's economy rather than any actual governing he did. While some find his personality to be unique and believe his inclusion to be an interesting representation of a ruler not considered "effective" in the traditional sense, just as many players (Many of whom are German themselves) are outright baffled that Firaxis ever thought to include him over the likes of more traditionally competent and respected German leaders such as Frederick the Great or Bismarck.
On a more individual level, the inclusion of the Cree in Rise and Fall has received divided reactions among actual Cree people. Some, such as the singers who performed the civilization's theme song, one of whom is a direct descendant of Poundmaker, were overjoyed to see themselves in the game; others, including notable chief Milton Tootoosis, felt including them was inappropriate in a game based around imperialism, something they were victims rather than perpetrators of in real life. Complicating this further is that many civs in the game have been victims of imperialism at some point in history (with some—such as the Aztecs, the Inca, Egypt, India, and China—having been both victims and perpetrators at various points), so the Cree are hardly unique in this case.
It's also worth noting that this wasn't the first time that the game ran into controversy over Native American representation. The Pueblo were considered for Brave New World, but ran into opposition from the Pueblo leaders, as visual depiction of their historical heroes are considered taboo in their culture. As such the Shoshone were included as a replacement.
The inclusion of a climate-change mechanic in Gathering Storm set off a new wave of arguments. In general, there were three camps that came about as a result of the mechanic's inclusion: Those who enjoyed the mechanic for providing some added flavor to certain civilizations that historically took advantage of certain types of climate (Such as Egypt and Russia, both of whom gain a buff in Gathering Storm to directly take advantage of the new mechanic) and bringing some added strategy to the game by forcing players to either play around mitigating disasters or even taking advantage of them, those who liked the idea in concept, but found its inclusion to be clunky and lacking in the depth it intended to provide, and those who disliked the idea from the start for being what they saw as an uncontrollable, random factor that may end up destroying your yields and ruining your city planning through no fault of your own.
to accusations of sexism and ignorance about the role women have played in history.