I'll let the pictures do more of the talking, starting with a more primitive view than I-80 currently allows:
During the summer months the view would be largely obscured except in nearby exposed outcrops, leading to a more dramatic view as one suddenly came upon the river and found the gates to a world further north and west ahead. In winter, though, seeing the gap filtered through the trees and wondering what could give the mighty Appalachians such an interruption would surely only heighten the excitement of finding such a place. Think about this in light of the fact that in the majestic forests of early colonial times, the trees were often as strong a selling point as the landmarks. A great ridge ahead would not come as a huge surprise to one who had already been given a taste of Appalachia on a trip into the backwoods, but a conquering sky like this? Definitely a distraction from the trees. Grandeur. Ease of passage. Opportunity.
Surely even the most economically motivated explorer would have stopped making marks on the map for a little bit, though. Pressing inland from incredible beaches, vast swamps, towering forests, and even a little bit of prairie patches, one suddenly came across rock and lots of it.
One would also see the open scale of some of those trees previously seen only from strictly below.
Then the land would be moved from mystery to frontier, and later considered a patch of hard to develop land between the prosperous coast and the fertile Lakes and Midwest. Grander vistas out west would become the new frontier and the Gap and places like it still a convenience, but also more of a memory of a difficult past overcome. What's the Gap in the face of so many deeper western canyons? Well, for one, I doubt that many people who pass through here don't at least temporarily feel small and a part of something greater. At any rate, the Gap is certainly more impressive a welcome sign to either Pennsylvania or New Jersey than some road sign.