I spent the weekend in Shanghai a couple of months ago and used the Metro to get around. It was modern, clean, on time, easy, and cheap - around €10 for an unlimited 72 hour pass. I was astonished by its sprawl, some lines over 50km and one close to 100km. It felt like it dwarfs London's tube. Criticisms? It was clearly at or near capacity, which I guess explains the rapid growth. There was a mass of security theatre…
That is just China in general. Their only card based payments for quite some time was UnionPay. Many places were cash only though. In the past 2-3 years electronic payments through WeChat or Alipay have absolutely exploded and nearly every business accepts it as payment in major cities. Unfortunately as a westerner these payment methods are mostly inaccessible, so cash payment remains the only feasible way to pay for most things.