Robert E Lee was one of the smartest military leaders in history.
Most people don't know this, but at the beginning of the Civil War, before Virginia joined the South, Abraham Lincoln asked Lee to lead the Union Army.
He won many battles where he was greatly outnumbered, such as Chancellorsville and Fredericksburg.
Lee was personally opposed to slavery (I think one of the biggest mistakes in world history was bringing African slaves to North America, and white people have paid a terrible price for it, especially in recent decades).
People think the Civil War was about slavery, but Lincoln's Emancipation Proclamation actually came two years after the beginning of the Civil War. Slaves were really only important to the economies of the cotton states like Alabama, and slavery wasn't really a major issue in states like Virginia.
The Civil War had more to do with economics and the North wanting to impose it's will on the South than about slavery.
There are two great movies on the Civil War I recommend:
Gods and Generals and G
ettysburg.