Shanghai Metro is a lovely bright airy place. If you are on it during the rush hour though it’s hell on earth. 
You have to move as one body of people. Chinese are famously inconsiderate, have no care about other people around them or the impact theire decisions have on those sharing the space with them. Therefore it is not surprising although it is really annoying that some people stop walking when they get off the bottom of the escalator which causes panic amongst the huge mass of people arriving at the bottom but with nowhere to go.
Only once at Central Avenue and at People’s Square at rush hour have I seen people queueing to get on the train. Unlike the old London system, being a new undreground system it has been built to cope with the numbers of people 
living in this vast city and so even when there’s no room to move independently of the other commuters it is still bearable. The carriages are light, air conditioned with loads of head room.
One disadvantage of using the Metro system in Shanghai, which you get less of in Nanjing, is the number of beggars. There are several types. There’s the blind, deaf, dumb ones who are often alone and osmetimes with a carer who leadds them along the carriage ringing a bell or playing a foul sounding “musical” instrument.
Then there’s the more common one – the women with suckling child. They crawl along the carriages holding their baby often stopping to let it suckle. They do this even when the child doesn’t want to and they always do it near women who might be sympathetic.
Compared to other world cities there are not a disproportionate number of beggers but because the Metro system has a concentration of people they often hang out there. And they always target westerners.