I found this book valuable because it shows how Trotsky was able to defend the revolutionary perspectives of Lenin under the difficult conditions of isolation and exile. Stalin and the bureaucratic layer he represented were strangling the voices of authentic Marxism, advancing the narrow-minded idea of socialism in one country, and stifling all criticism. The bureaucratic gang was putting its needs ahead of the needs of workers around the world in the same way that, years later, the heirs of Stalin cut off all aid to Cuba (after doing nothing for Algeria and the Congo and almost nothing for Vietnam). But the continuity of Lenin was preserved. This is a good book to read as you follow the class struggle today, including the internationalist role of Cuba.
Trotsky takes up broad questions of interest to revolutionary movements everywhere: from the economic foundations of post-capitalist society, to the fight for effective participation by workers and farmers in political debate and decision-making, to big challenges of revolutionary internationalism. You see him grappling with the complex questions posed by the degeneration of the Russian Revolution and its leading party, and the tactical challenges posed in waging a political fight at a time when it was still possible to return the party to its original, revolutionary course. You can learn a lot from his writings on world developments and debates over what revolutionists should do: revolutionary and class struggles in China, Britain and Germany, shifting economic and political relations among the imperialist powers, and much more.
I'd suggest studying this book along with some of Trotsky's other major writings, including The Revolution Betrayed, Leon Trotsky on China, and The Stalin School of Falsification. And for bringing these issues up to today's world, Capitalism's World Disorder: working-class politics at the millennium, and Their Trotsky and Ours, both by Jack Barnes.
The reader will need to buy "Credit Derivatives and Synthetic Structures" by Tavakoli to get insight into these products.