150 years ago today - the day after the battle
First, some things missing from the film
I already talked about day 1. For day 2, the film focuses almost entirely on Joshua Chamberlain and the 20th Maine on Little Round Top. So what's missing? Well, lots.
Chamberlain's Regiment was part of Strong Vincent's Brigade. Vincent's Brigade was rushed in to cover Little Round Top after General Warren discovered it was uncovered and that the Confederates had figured that out. All the regiments in Vincent's Brigade were heavily involved, and Vincent himself was killed that day. Now why was Little Round Top uncovered? Because General Dan Sickles had ignored instructions and moved his forces forward from Cemetery Ridge to the Peach Orchard and the Wheatfield. Sickle's forces were not sufficient to extend to Little Round Top, so they were anchored on Devil's Den. There was intensive fighting in the Peach Orchard, the Wheatfield and Devil's Den, none of which is covered in the film. And the film doesn't cover any of the fighting going north along the line, wrapping around Cemetery Hill and Culp's Hill.
Day 3 in the film is all about Pickett's charge, but ignores all kinds of other fighting that day.
Context
Generally missing from most Gettysburg discussion (film or otherwise) is context. Meade is often criticized for failure to pursue, but actually the Army of the Potomac followed Lee for 10 days, almost trapping Lee against the Potomac River. Meade seems to have come up about one day short on catching Lee, but Lee's escape wasn't exactly a cakewalk.
Some recommended books
Gettysburg: The Last Invasion Allen C. Guelzo
Gettysburg Stephen W. Sears
Plenty of Blame to Go Around: Jeb Stuart's Controversial Ride to Gettysburg Wittenberg & Petruzzi
One Continuous Fight: The Retreat from Gettysburg and the Pursuit of Lee's Army of Northern Virginia, July 4 - 14, 1863 Wittenberg, Petruzzi & Nugent
Protecting the Flank at Gettysburg: The Battles for Brinkerhoff's Ridge and East Cavalry Field, July 2 -3, 1863 Eric Wittenberg
Gettysburg's Forgotten Cavalry Actions: Farnsworth's Charge, South Cavalry Field, and the Battle of Fairfield, July 3, 1863 Eric Wittenberg