We love them. We hate them. We spend millions as a society to go watch them and then those of us who can see past the end of our nose make fun of how ridiculous most of it was.
For this argument, let us talk about those that claim to be based on a true happening, not fantasy such as Lord of the Rings, The Hobbit, or even the 300 films as they are actually based off of a comic book which took the story and fantasized it.
Rather, let us look at movies such as "Helen of Troy" such as this video explains quite a few errors:
Then we get into the King Arthur mythological movies. Now, they claim to be based off of historical and archaeological evidence, but where? Where did it, in any of the texts, have Dagonet be a bad-ass knight as they portrayed in the 2004 Clive Owen version? Because from the texts, Dagonet was actually a fool made knight in jest by Arthur. (read more about that here)
A good movie, and one that closely follows the facts (as far as close to facts relates to Hollywood anyways) is "The Messenger: The Story of Joan of Arc". It, out of almost all of the medieval movies, follows in truth closest to the facts of the topic better than most others. However, it too comes with criticism for its dialogue as found here:
The bottom line is this Hollywood, we are watching, so make us believe, please?!