The slaughters at Franklin, Cold Harbor, Fredericksburg, and Pickett's Charge were horrendous to say the least, but each assault was preformed and fought out differently.
Pickett's Charge is much more like the attack on July 3 at Cold Harbor, both lasted a short amount of time, very few men broke through, and both saw similar casualty numbers. Pickett's Charge stretched only for about half a mile in length and in width, whereas the attack on July 3 at Cold Harbor stretched for almost a mile and a half in width.
Fredericksburg was divided up into two separate fronts - Marye's Heights and Prospect Hill/Slaughter Pen - but Marye's Heights is known for its separate, piecemeal attacks by each of the three divisions of the II Corps at a time as they melted away one by one. None of the Federals attacking Marye's Heights reached the stone wall.
The thing about Franklin is that you had 5 divisions, stretching about a mile in width, converging in on a line of works less than half a mile in width. That's what made Franklin such a fierce and chaotic battle, so many men were stacked in around such a small area and were blown away in only a few hours. You had around 20,000 Confederates converging on a point less than 3,000 feet in width (not counting Bate's Division attacking the Federal right later).
Because the brigades were so stacked up, the assault continued for as long as it did; as one brigade would melt away the other behind it would run up and get shot to pieces. The men would retreat and regroup, or take their place in the next regiment running up and attack again. To the Federals, it gave the impression that the Confederates were being sent in almost piecemeal. Another thing about Franklin is the large amount of close range combat over the earthworks. Unlike any of the other three assaults, the Confederates managed to reach the Federal works all across the line, but were stuck outside in the ditch and fought right over the works.