Not attacking up mile-long hills well-covered by batteries may also have had something to do with it....Lee might have learned from the six charges up Malvern Hill that failed in 1862, during the Chickahominy campaign, but then he did it again at Gettysburg. Ouch.
By way of explanation, this was a habit officers on both sides had acquired in the Mexican war, when they got away with assaulting prepared positions defended by infantry and artillery repeatedly, because of the Napoleonic weapons they were facing and the inexperience of most of the Mexican troops. They wouldn't have gotten away with it against Wellington, but they weren't facing Wellington. So they, and Bobby Lee particularly, imbibed a deadly lesson. Thus Edward Bonekemper, How Robert E. Lee Lost the Civil War (Sergeant Kirkland's Press, Fredericksburg, Va.: 1998).
Yep. Lee was good as Civil war generals went, but was certainly not the genius as Southern Civil War mythology has painted him. He was uncommonly good at assessing the tactical situation, making good use of terrain, and then doing what the enemy least expected.
At Getteysburg he experienced a major lapse. Longstreet lobbyed hard against engaging the Union at Gettysburg, because he saw how much the ground favored the Union forces. But Lee's arrogance and disdain for his opponents, combined with the desire to bring the Union to the negotiating table got the better of his tactical sense (a good general doesn't waste his troops and listens to the council of proven subordinate commanders). The only thing that saved the Army of Northern Virginia from complete annhilation was the failure of union forces to pursue him in retreat. McClellan could well have ended the war then and there if he had.
After the war, Longstreet, who was arguably the better general, made the mistake of letting his opinion of Lee's actions at Gettysburg known publicly. The south turned on him rather than believe anything ill of Lee. Longstreet was shunned by his friends and died a broken man because of it.
Lee is the sacred cow of the south. Criticising him to a southerner is worse than blasphemy, and they will always point you to some book written to support the myth rather than the facts. They also forget that his many early victories were won in battles against very incompetent Union commanders leading green troops that could barely handle a musket - while most southern soldiers came to the Army of Northern Virginia with exstensive experience handling firearms and time in the saddle.