What I liked about the GAP was the industrial and labor history near Pittsburgh, the mining memorials and other remnants of our industrial and coal-fueled past. The GAP is a rolling history lesson in many ways. Plus the tunnels and bridges were very cool too; I'm always amazed at human ingenuity.
I also liked that I could fly my drone on the GAP. Can't fly on the C&O.
And the bridges and tunnels too. Lots of interesting things to observe ponder.
Here's Chapter 3 of my trip, from Ohiopyle to Meyersdale.