As history it was sketchy, but what movie isn't. Its frankly amazing to me how much Milius got right. Krags, potato diggers, the correct Gatilings in .30 US, a Hotchkiss revolving cannon. Black Jack Pershing and the 10th. Tiffany and Parker. Leonard Wood and the New York Society Swells. William Randolph "I'll provide the War" Hearst. And Bryan Kieths Mckinley, though almost an exact opposite of the real patrician McKinley, was a hoot to watch.
It was entertaining, and it made folks think about the forgotten war that set the stage for the 20th century. And much like "Tombstone" served to interest folks in SASS, "Rough Riders" was in many ways one of the things that got like minded folks talking about, and forming, the GAF.