My first response was more strategical "what if" related.
In terms of actual battle actions, I have two places on the battlefield that I stand in awe at. They were both important actions in a battle of many strategically important actions.
The first is Day 1 action. I stand near the 19th Indiana, 24th Michigan and 26th NC monuments on Stone/Meredith Avenues. The delaying action of the Iron Brigade played a significant role on Day 1. Ken Burns in his epic Civil War tv series on PBS said that compared to Day 2 and 3, the first day was just a skirmish (something like that anyway). But look at the casualty figures for the Iron Brigade and the 26th NC (I know they were in PPT charge too) and you will see that the battle there was not a skirmish. I would love to know if that area had the highest combined casualty rate in the entire CW.
The second action was the charge of the First Minnesota. There were thousands of heroic actions at Gettysburg, but none strike me in awe like the First Minnesota charge on Day 2. Imagine the courage it took to for that small regiment to charge when they were so badly out numbered. Why this charge isn't better known is a mystery to me.
From their monument:
On the afternoon of July 2, 1863 Sickles' Third Corps, having advanced from this line to the Emmitsburg Road, eight companies of the First Minnesota Regiment, numbering 262 men were sent to this place to support a battery upon Sickles repulse.
As his men were passing here in confused retreat, two Confederate brigades in pursuit were crossing the swale. To gain time to bring up the reserves & save this position, Gen Hancock in person ordered the eight companies to charge the rapidly advancing enemy.
The order was instantly repeated by Col Wm Colvill. And the charge as instantly made down the slope at full speed through the concentrated fire of the two brigades breaking with the bayonet the enemy's front line as it was crossing the small brook in the low ground there the remnant of the eight companies, nearly surrounded by the enemy held its entire force at bay for a considerable time & till it retired on the approach of the reserve the charge successfully accomplished its object. It saved this position & probably the battlefield. The loss of the eight companies in the charge was 215 killed & wounded. More than 82% percent. 47 men were still in line & no man missing. In self sacrificing desperate valor this charge has no parallel in any war. Among the severely wounded were Col Wm Colvill, Lt Col Chas P Adams & Maj Mark W. Downie. Among the killed Capt Joseph Periam, Capt Louis Muller & Lt Waldo Farrar. The next day the regiment participated in repelling Pickett's charge losing 17 more men killed & wounded.
So many important actions, so little time.