There are a few interesting nuggets that really shed light on Longstreet's actions at Gettysburg.
Lee demonstrably didnt understand the Federal position the morning of July 2nd. The incident where he corrected Longstreet as to the intended position of McLaws is illustrative. Longstreet told McClaws to align parallel to the Emmitsburg Road, Lee interrupted and said no, he wanted McLaws perpendicular to the road. Both divisions were to attack 'up' the road to strike the Federal flank anchored on Cemetery Hill.
The problem was, the Federal flank didn't follow the road at all. At dawn the federals occupied a line directly down Cemetery Ridge and anchored at the foot of Little Road Top (although pickets extended across the road). Emmitsburg Road diverges southwest of Cemetery Hill. Had Longstreet attempted what Lee indicated _at any hour of the July 2nd_ he would expose his right to the 3rd Corp, the arriving 5th Corp, and elements of the 2nd corp, with all their guns on the ridge. The order to align that way would never have been given once it became apparent how the Federals were actually disposed.
IE- there was no angle or salient for Longstreet to attack where Lee ordered.
Whats interesting is that it would seem (giving the initial instructions Longstreet gave McLaws) that Longstreet had a better grasp of the Federal position from the beginning, and was developing a rational plan to deal with it. Without decent reconnaissance, both men were making educated guesses on what the Federals were trying to accomplish, and like much of the battle, the roads are the key. If you assume the federal reinforcements will be coming up the Emmitsburg Road (as the 3rd Corp had), the Federals would be extending to protect that vital avenue. On the other hand, if you believe the reinforcements would be arriving via the Tanneytown Road and/or Baltimore Turnpike (as indeed the 5th and 6th Corp did), the Emmitsburg has no relevance aside from _some_ areas of higher ground adjacent (The Peach Orchard).
Whats even more interesting is that Sickles obsession with those bits of high ground were probably influenced by this issue as well. Several 3rd Corp units and the corp ammunition train were following up the Emmitsburg but had no arrived as of mid-day. Keeping command of the road would be an issue with Sickles, and perhaps in his mind that was the supply line of the army.
Meade, on the other hand, saw no value in the road and instead occupied the arguably better (and certainly shorter) line from cemetary hill down the ridge to the round tops. This was closest to his reinforcements and had the better road network behind it to shift units. Any attack on any part of that line would be open to enfilade from either or both ends (unless the Rebels could attack the entire line at once).
At the end of the day- there was simply no way to attack Cemetary Hill from Longstreets position. Any attack made would either have to be a frontal assault Eastward, or detaching from Hill and seeking out the Union Left below the Roundtops (which would have run face first into the arriving 6th Corp). Longstreets frustration take on a slightly different shade knowing that his orders were untenable. He may have foot dragged to get his corp into position, but he certainly attacked with an unrivaled fury, and managed to enterprise a plan that nearly split the Union line in 2 with only 2 divisions and middling help from Anderson's. Longstreet didnt have a single regiment that wasnt heavily engaged that afternoon. And another brigade or two in reserve might have given him the strength to break the line entirely. Not a bad days work.