I didn't think Lee was that good of a general. Many of his successes were the result of stupid union generals or very risky chances he took. The union, with far more men, material, etc., did not have to take "risky" chances and was more conservative. Too conservative.
Lee's biggest mistake was attacking uphill against entrenched enemies at Gettysburg. General Longstreet tried to dissuade him, pointing out it would be far better to leave and go around the union army to take up a position atop a hill closer to Washington, and let the union army beat itself to death attacking them. Longstreet even told Lee that his scouts had identified such a hill. But Lee would have none of it. Thus the disastrous charge which the southern historians, incapable of blaming Lee, called "Pickett's Charge." Lee should have remembered the recent battle at Fredericksburg, where the union suffered defeat attacking entrenched Confederates up a hill.
After that it was simply a matter of Grant having more men, supplies, and guns than Lee. But Jeff Davis thought the South could win almost to the end. His reasoning: The South still had a lot of unconquered territory and the northern people would get sick and tired of the war. He wasn't alone in thinking that. A year after Gettysburg, Lincoln was convinced that he (Lincoln) would lose the 1864 election and President McClellan would let the South go.
