Lee was one of the greatest Napoleanic generals. Unfortunately for him and the South, the Civil War was the first modern war. Napoleanic tactics had become obsolete.
Imagine if the Gatlin Repeating Gun, metal encased ammo, breach loaded rifles, etc were used against the Southern gentlemen at the First Battle of Manassas (Bull Run)
http://www.civilwarhome.com/1manassa.htm rather than in the latter half of the Civil War.
Jackson would have been mowed down along with his valiant but misled men. And "Stonewall" would have been replaced with "Pinebox" Jackson, going down into history as the true and original Pickett's charge.
Imagine if Newport News was successfully defended against rebel troops and the CSS Virginia remained the USS Merrimack
http://www.history.navy.mil/photos/events/civilwar/n-at-cst/hr-james/9mar62.htm And imagine if Robert E Lee saw beyond regionalism, saw beyond a state and saw a greater goal.
Imagine if the southern planters were not greatly indebted to the europeans and the northern states.
Imagine a sustainable mixed economy with human dignity/freedom rather than short-term illusions of greatly exaggerated wealth on the backs of share-cropping Irish/Scots/Welsh and slave labor.
Imagine if the southern states remembered the folly of the Whig/New England seccessionism in the early 1800's and considered the actions of some rebels as dead-end foolishness.
This nation would be ever greater! Sorry I won't celebrate Robert E. Lee.