Hey ho
Not easy to answer. The pure size and diversity created a big fascination. When I lived in Beijing I got a very warm welcome from my colleagues and I found friends all over China. I was always interested in traditional things, such as arts, language, behaviour and so on. And I always got positive feedback for my wish to watch "behind" the things; not only being a foreigner and a tourist. I loved to make jiaozi with the families I visited and play cards or even try to play erhu. Actually it is everything - too much to tell in a short message.
Since I am from Berlin and Change was always a part of my live, I can feel a similar vibe in China, with all it positive and negative aspects. Hope this gives you an impression ^_^