I visited the Great Wall of China on two occasions: first in 2004 near Beijing and the second time in 2007 near Dunhuang in Gansu Province.
To make the first trip, I joined one of the daily 50 yuan tours that start from Qianmen. The guide started chattering (in Chinese of course) right from the start and didn't stop for the first hour (without breathing, was my impression). Besides me, our group consisted of mainly male Chinese daytrippers. That gave them some interesting photo material - themselves and me on various parts of the Wall.
Our first Wall-stop was at Juyongguan. I was really happy when I got off the bus: so this is it! One of the most exciting moments in a travellers life. First impression: it's really very steep to walk to one of the watchtowers. And it's a really strange feeling to stand here: like the Taj Mahal, you're so familiar with its looks that you don't know what to think of it.
The other stop was at the infamous Badaling-site. Here it's all quite touristy, but not too bad this time of year. They also have a Great Wall museum where they exhibit (among other not too interesting stuff) the Unesco World Heritage inscription document.
A very different experience is visiting one of the wall sections in the outer provinces. There are a few of them in Gansu. On a cold November morning, I headed out for the Yumen-pass. Close to that monument of Silk Route fame is a stretch of the Great Wall dating from the Han dynasty. Desert, desert is about the only thing you see here for hundreds of kilometers. And then there's the outline of a wall and a beacon tower. The wall here was made of loess and reed, which has been preserved well.