I asked our guide at Gettysburg if The Killer Angels was a good intro. He vehemently rejected it, saying it relied too much on (Longstreet's ? memory glitch memoirs). He recommended this instead. I concur.
Unfortunately my memory for names is a bit on the foggy side, and there were times I wished the names were color-coded so I could tell who was who, but within a couple of paragraphs I had the scene correct anyway.
FWIW Tucker concludes that the biggest contribution to the Confederate loss was Lee's microscopic staff, which left him unable to keep on top of what his subordinates were actually doing. I've heard it said that victory goes to the side that makes the fewest stupid blunders; there were plenty to go around at Gettysburg.