He was a good General in all aspects. That's why his campaigns are studied even to this day by military historians. He made mistakes, see Picket's Charge as one of the major ones, but overall taking the fight to the enemy likely prolonged the Civil War a couple of years.
Look, there are several "enemies" of America that historians could and should respect and study. Rommel for example. Heinz Guderian is another. Vo Nguyen Giap is one. Georgy Zhukov is another. Geronimo is one that gave the US Army fits for many years. J.E.B. Stuart and Stonewall Jackson are two exceptional Confederate commanders that should be studied.
One needs to have an unbiased view of military history to say "yeah, these were great Generals because of X, Y and Z." Even you can see the media is trying to drudge up views of racism by omitting portions of Trump's speech.