I abhor war movies, but this one is not really a war movie. Rather, it is a character study of one of the most interesting figures of the 20th century, wonderfully played by George C. Scott.
Since the movie purports to be a true story, I thought it useful to compare the events in the film with Patton's actual life, as recounted by Wikipedia's very detailed biography.
1. Near the start of the movie, it depicts Patton as orchestrating the re-assignment of General Bradley as his assistant in the North Africa campaign, so that he would no longer be "spying for Ike". Wikipedia agrees, saying "Patton had Bradley reassigned to his Corps Command as deputy commander. Thus began a long wartime association between the two diverse personalities." This complicated relationship is a major theme in the movie.
2. When Patton takes over the forces in North Africa in the movie, he instills discipline, which includes requiring everybody to wear steel helmets, even the doctors in the operating room. Wikipedia again agrees, saying "Patton required all personnel to wear steel helmets, even physicians in the operating wards, and required his troops to wear the unpopular lace-up leggings and neckties. A system of fines was introduced to ensure all personnel shaved daily and observed other uniform requirements. While these measures did not make Patton popular, they did tend to restore a sense of discipline and unit pride that may have been missing earlier."
3. Concerning the infamous "slapping incident", Wikipedia states that:
When General Eisenhower learned of the incident, he ordered Patton to make amends, after which, it was reported, "Patton's conduct then became as generous as it had been furious," and he apologized to the soldier "and to all those present at the time, "After the film Patton was released in 1970, Charles H. Kuhl recounted the story and said that Patton had slapped him across the face and then kicked him as he walked away. "After he left, they took me in and admitted me in the hospital, and found out I had malaria," Kuhl noted, adding that when Patton apologized personally (at Patton's headquarters) "He said he didn't know that I was as sick as I was." Kuhl, who later worked as a sweeper for Bendix Corporation in Mishawaka, Indiana, added that Patton was "a great general" and added that "I think at the time it happened, he was pretty well worn out himself." Kuhl died on January 24, 1971.
The film omits Patton's personal apology to the soldier, and presents him as half-heartedly apologizing to the entire army en masse, after being instructed to do so. Thus the film omits the fact that Patton on his own made some effort to make his amends.
4. After the slapping incident, the movie makes much of the Germans being mislead by Patton's deployment in non-combat areas. This seemed to me to be the most artificial of the movie's depictions. However, Wikipedia supports the movie depictions, saying that "During the 10 months Patton was relieved of duty, his prolonged stay in Sicily was interpreted by the Germans to be indicative of an upcoming invasion of southern France. Later, a stay in Cairo was interpreted as heralding an invasion through the Balkans. German intelligence misinterpreted what happened and made faulty plans as a result."
5. During the 1944 offensive into Europe the movie depicts Patton as ordering his chaplain to come up with a prayer for good weather. This seems pretty artificial; however, again the movie got it right. Wikipedia states that: Needing just one full day (24 hours) of good weather, Patton ordered the Third Army Chaplain, (COL) James O'Neill, to come up with a prayer beseeching God to grant this. The weather did clear soon after the prayer was recited, and Patton decorated O'Neill with the Bronze Star on the spot. Following this, he continued ahead with dealing with the German offensive and von Rundstedt.
The battle scenes and campaigns seem to be factual also, so overall I would say the film is much more factually accurate than many film biographies.