China rail have pretty bad hygiene at that time. The passengers freely throw their trash on the floor and out of the window. The attendants swiped the floor every few hours. Every time they pushed a mountain of peanut husk away. There was a peasant family on board with a baby. The baby needed to relief. So the parents held him up to have him shit on the floor. The attendant saw it and really lost it. She scolded the hell out of the family.
But even so, it was a wonderful experience. The Chinese landscape is nothing short of awesome. And the culture that unfolded was completely unknown to me, so constantly interesting.
One thing that really made me take notice was the wide range of people. On the way to the Shanghai train station, we had walked by a Lamborghini dealership (I don't recall ever having seen even one of these in the USA) - there's a not-insignificant population of filthy rich people in and around Shanghai. But on the train we saw people peasants using an ox to plow a rice paddy of only a fraction of an acre. The degree of inequality was hugely wider than America or any other nation I've seen.
EDIT: the Shanghai airport maglev train was an interesting experience just to say I've gone 300+mph on a train, but otherwise totally boring.
I’ve also done Shanghai to Changsha and Changsha to kunming like that. It gets interesting west of hunan.