I don't pretend to know everything about Leftist theory, but it doesn't seem complicated. Also, I'm from the UK, where things different enough from the US that it is worth mentioning.
I don't care for any governmental system that exists now. They are all based on state control of individual freedoms. I am essentially an Anarchist, but with "protection from a distance" meaning something automated and trusted that protects people from harm and control by others, while allowing everyone to do as they please. I realise this is a futuristic fantasy but it is worth aiming for imho.
Before I critique communism further I want to make it clear that I know western democracies are corrupt, some extremely so, and that corruption is driven by the super rich. (Oil, tech, arms, other evil shit).
The nature of corruption is very different between western Democracy and communism. In the west it mostly goes public (and not much gets done about it apparently), but changes are made and things do generally improve in the long term. In china it is all done behind closed doors, and is about protecting bureaucracies. For me the "public vs "private" behaviour is the most important difference. When issues are public is there a chance for the public to have a voice, but when it's all behind closed doors what chance do the public have?
Also, it is about individual freedoms to do and say what you like without fear of state interference, which communist states don't have a good reputation for. I'm sure you can think of a few subjects you can't discuss in China. Why is that? What subjects can't you discuss in the UK?
Granted, right now western culture is going through a period of hyper conservatism with freedoms being oppressed, but this is a battle ground with voices from every corner speaking out, which is impossible in a communist state. How would this be dealt with in China? Either way, I am hopeful this too shall pass, and we'll move away from the extremes of capitalism (once the current generation of old people die off)
Regarding my idealism around getting rid of money. T I know this is a problem we can't solve today, but I don't think it's far away This is a side topic for another post I feel. I'll write up my thoughts and post it.