You may find it a different story from the one you learned in school. There have been many versions of that battle and that war. I have therefore avoided historical opinions and gone back primarily to the words of the men themselves, their letters and other documents. I have not consciously changed any fact. I have condensed some of the action, for the sake of clarity, and eliminated some minor characters, for brevity; but though I have often had to choose between conflicting viewpoints, I have not knowingly violated the action.Shaara also cites Stephen Crane's The Red Badge of Courage as an inspiration for his novel -- that reading history isn't enough to induce the feeling of being there. Of course, this raises the question as to what liberties Shaara took -- what minor characters he eliminated or condensed, and why was this done? (Although, who needs a dozen different aides to a general when one will do?)
The Killer Angels is split into chapters in which the narration is focused on one man, from a third person perspective. I believe this is the best way to convey the scope of the planning, buildup, and execution of the battle, as Shaara rotates the viewpoint with each chapter (although the narration remains third person omniscient). The biggest criticism of this usage is that the thoughts of the most recurring characters (Longstreet for the Confederacy, and Colonel Chamberlain for Union) can get repetitive -- Longstreet constantly despairing of his inability to persuade Lee to engage in a more defensive posture, and Chamberlain doting on his younger brother, Tom. It is precisely because of this narrative structure that The Killer Angels succeeds as a humanistic portrait of the battle, rather than a historical analysis -- real people can be tedious and repetitive.
While I don't have the historical chops to go into whether or not Shaara's narrative is a) faithful to the sources he worked from and b) in line with what modern historians believe, I feel that I should point out that after the battle begins, he neglects to mention much beyond Little Round Top (because that's where Chamberlain was, and where Longstreet, on Lee's orders, attacked) and Pickett's Charge (because Longstreet and Chamberlain were again both involved). While the action on Little Round Top and the Federal center were not inconsequential to the battle, other areas of engagement are glossed over. So while the novel is large in scope, it seems almost narrow here.
The Killer Angels is a worthwhile, easy read, and certainly made me want to look more into the Civil War in general, and the Battle of Gettysburg in particular. In that respect, it is a smashing success. Is it a worthy Pulitzer winner, though? Out of the winners I have read, I would rank it next to last, ahead of only Jhumpa Lahiri's Interpreter of Maladies.