This book tries hard to summarise to a more accessible language the fundamental concepts of Marxism without tone down the scientific and revolutionary characteristics.
This is probably a more appropriate introduction to Marxism and Communism than the (dated) Communist Manifesto. It clearly lays out the fundamentals of Marxist economics while situating Marx's work in the context of the state capitalist nations of the People's Republic of China, the USSR post-Lenin, etc. The strength of the book is it's focus on economics and the analysis of classes in society. However, the book's last chapter about what communism may look like is a bit old-fashioned and does not reflect current debates about whether police should exist within a society by/of/for the working class.
The book also did a good job of capturing the many voices / perspectives within Marx's work. Not just highlighting his economic analysis but also bringing forth his humanism, his complex views of alienation and exploitation (both from an economic perspective and a more subjective experience perspective—i.e. Marx's humanism)
I would definitely recommend it to people who do not wish to read Capital (but I would add the caveat that Capital is much less dry and more entertaining than many people think of it. For example: Marx's dramatic personaes of capitalist society which form a thread/subplot to his analysis of a sort of stage production).
This is among the best introductory summaries of Marxism out there, especially economic basics. This along with marking out the foundations (1946 prometeo, ICP) serve as my go to suggestions when anyone asks me for beginning into Marxism (besides obviously Marx and Engels). It deserves credit for not dulling down any of Marxism's aspects, straight to the point precise and rigorous summaries of fundamentals of labor power, wages, constant variable capital, accumulation, tendential fall in rate of profit and demonstration of the Marxist method in reading history. As an added bonus, it also includes a deepened rendition of the immediate program of the revolution (as the one developed by the ICP, or the manifesto)
Robingoodfellow produces very thorough critiques, writings on economics and crisis theory in the tradition of programma comunista/ICP while claiming to stick only to Marx and Engels, which I can respect even if some of their other works, political readings (national question, the democratic republic etc) are to say for the least very questionable.
Highly recommended is also the part "Appendix 1: The Function of the Middle Classes" from their other book "toward the foundation of crisis