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.
Artistic License-History: John Green skips over the Protestant Reformation in World History and the Space Race in US History. The closest we get to the latter? An image in the introduction briefly mentioning the Apollo Program and a still image of an Astronaut in the episode on America in the 1960s. And what does Green make a video of instead? Captain Cook. Is Cook an important figure? Debatable, but it is certain that he isn't as important as the Reformation.
Although the Cook episode is very important in teaching about the importance of understanding how shifting the context upon which history is viewed essentially changes the history itself. And the running theme of the history episodes is that understanding the context and the "hidden histories" not elaborated in textbooks is much more important than just listing out the facts.
In part to respond to this criticism, they have since announced Crash Course World History 2.
Broken Base: The episode "Battles of the Civil War" has proven to be this. Some viewers accepted John's basic listing of major battles of the Civil War as a good Take That, Audience! towards those who ask for more military history on the show and acceptable filler to pad out his paternity leave, especially since the following two episodes were also about the Civil War and contained much more analysis and details. Others dislike the episode, either because they see it as disrespectfully trivializing the entire field of military history or because an intentionally boring show is still boring.