I've never seen left communism's history summarized so briefly and effectively. Well done, Martin.
I admit that I've long been sympathetic to Bordiga's characterization of the Chinese, Vietnamese, and North Korean transitions to Stalinism as "bourgeois revolutions with red flags," even though I don't think it's literally true. (Well, perhaps in China and Vietnam one could say it's "true but declared prematurely.")
One left communist that everyone should read: Paul Mattick, especially his book MARX AND KEYNES. If nothing else it provides a convincing rebuttal to the "monopoly capitalism" school of MONTHLY REVIEW magazine, even though the end of the gold standard makes the book somewhat outdated.
And the Dutch-German left communists did have one valid point in the debate with Lenin; I can't remember the exact essay where they discuss this, but they overtly rejected the emphasis on "iron proletarian centralism" in Lenin's LEFT-WING COMMUNISM, AN INFANTILE DISORDER, and with good reason -- as spelled out in “The Organizational Structure of the Communist Parties, the Methods and Content of Their Work” (Communist International resolution, 1921), "iron centralism" leads to the creation of sects. This has been just as much true in Trotskyist groups as in Stalinist ones.