Just read this today (It was just published on 3 May 2016, btw, so this is definitely the most recent scholarly work on the topic):
Frank Dikötter is somewhat polemical in some parts of his presentation, but I previously read the work Tombstone by Yang Jisheng covering the Great Leap Forward, and he and Dikötter describe almost identical mechanisms within the Chinese Communist Party and the disastrous consequences of them. So all in all, I would say it is a fair treatment of the subject despite the fact that Dikötter obviously has nothing but contempt for Mao (and I really can't blame him...)
The book also provides a good overview of the internal power struggles between the key players in the Chinese Communist Party: Mao Zedong himself, Mao's wife Jiang Qing (and her infamous Gang of Four), Zhou Enlai, Liu Shaoqi, Lin Biao... and the man who finally stopped the madness: Deng Xiaoping.
Anyway... The Cultural Revolution was nowhere as lethal as The Great Leap Forward (the latter killed at least 36 million people according to Yang Jisheng, and at least 45 million according to Dikötter, surpassing any other genocide in history). In comparison, Dikötter estimates that 1.5 - 2 million died during the Cultural Revolution.
However, the Cultural Revolution (and the Red Guards in particular) did almost incomprehensible damage to the history and culture of China. For instance, it basically wiped out the entire medical profession in large areas of China, because Mao had decided that formal education was unnecessary and contrary to communist ideology. Unsurprisingly, a lot of people then died from various illnesses and diseases.
Oh... and to summarize the book in a single line:
Communism is a disaster and Mao Zedong was a complete as*hole.