The subway train system in Shanghai is actually pretty good, it's cheap, fast, easy to use and it is definately the best way of getting around.
The first problem is that there are so many people using it, particularly now because it is a Chinese national holiday. There have been couple of stations that were so jammed full of people that shuffling was the only option. Try it at home, it takes ages to shuffle a couple of hundred metres. Peoples Square and Shanghai Railway Station seem to be the busiest. Turn up the temperature to 30+ degrees and then you've got the Shanghai subway experience.
The other problem is that people do not give way to others at all. A couple of times at Peoples Square I tried to get off the train where the platform was already packed full of people, all shuffling towards the train. I found myself being barged back into the train by the crowd waiting to board. Each time there wasn't an inch of a gap for me to squeeze through. So I, along with everyone else wanting to get off, barged into everyone boarding, sort of like a upright scrum.
Admittedly, Sydney is not the common courtesy capital of the world but at least in Sydney people boarding allow a bit of space for those wanting to get off.