This book was recommended to me by my step-father, who is mainland Chinese. He grew up during the cultural revolution and has plenty to say about it. He thought it was a good overview of the Party, and I enjoyed the read.

https://www.amazon.com/Party-Secret-Chinas-Communist-Rulers/...

They control their citizen's access to information, but from outside it's not difficult to get a relatively accurate picture. This book [0] for instance was quite helpful in understanding how the CCP controls the country and, as a result, how many things work in China.

[0] http://www.amazon.com/The-Party-Secret-Chinas-Communist/dp/0...