I have to say the National Park Service does an excellent job at these sites. I preferred Fredericksburg and Chancellorsville myself. At the first, the visitor center is by the partly still standing sunken road at the base of Mayre's Heights, at the latter is is very close to the spot where Jackson was shot. There is a walking tour of the 1st Manassas battlefield and a driving tour of the 2nd (although they overlap). I suppose Manassas gives a more general introduction to the war because it was the scene of the first 'major' battle. I didn't go to Spotsylvania or the Wilderness (near Chancellorsville) because as of last October they only had a small display shelter and self guided tour, as opposed to the expert guides on site.