One of the very few accounts in English of German idealism, this ambitious work advances and revises our understanding of both the history and the thought of the classical period of German philosophy. As he traces the structure and evolution of idealism as a doctrine, Frederick Beiser exposes a strong objective, or realist, strain running from Kant to Hegel and identifies the crucial role of the early romantics—Hölderlin, Schlegel, and Novalis—as the founders of absolute idealism.
It has been a while since I read it, but it seems to me that Paul Beiser's account of Fichte in German Idealism: The Struggle Against Subjectivism, 1781-1801 was worth reading.
[Edit: added inadvertently omitted "you".]
https://en.wikipedia.org/wiki/Frederick_C._Beiser#Works
Also, it's much easier to start with Hegel's lectures (on aesthetics, history, religion etc.) and just go read the Phenomenology & Science of Logic after one has a sense of his style and general philosophy. It's foolish to start by the most difficult texts.
And don't take Schopenhauer's criticisms of Hegel too seriously, as they are mostly due to personal misgivings and envy (Sch. couldn't stand Hegel's popularity, while Sch. barely managed to get any students for his classes).
[1] https://autisticmercury.com/2017/02/25/kantbots-critical-for...
The Cambridge Companion to German Idealism (I forget which year) is also highly recommended though I haven't looked into that myself.
Bryan Magee's book on Schopenhauer.
German Idealism/The Fate of reason by Fredrick Beiser.
Hegel and the Hermetic Tradition by Glenn Magee
Kant's Transcendental Idealism: An Interpretation and Defense by Allison
Plato: Complete Works by John Cooper is good
The Paidea series by Jaeger is amazing as is the four volume collection by Giovanni Reale if you're interested in ancient philosophies (like me)
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The 'phenomenological' school is considered important.
Making Sense of Heidegger by Sheehan
Merleau-Ponty's Philosophy by Hass
However I think most true Western thought is to be found in the great works of literature. Ovid/Dante etc. try reading Howard Blooms work "The Western Canon".
Personally I find most western philosophy quite turgid.
I haven't read Diamond, but I could understand, if you're a liberal academic and you see a text, almost like Nietzsche's Geneaology of Morals, that just says that the strong always conquer the weak because of totally contingent conditions, it will seem horrifying because, as a liberal, you genuinely believe in personal agency and social justice and all that fun stuff. But go back and actually read Marx, go and read all your favorite Frankfurt school thinkers: they will say, the conditions that we have been placed in are a real illusion of nature: even if the so-called nature of things is a construction, it is one where the reality of it is undeniable for us. Therefore, the goal of critique, even in that Marxian, Kantian sense, is to raise consciousness to shatter that real illusion precisely by illuminating this so-called "natural" process.
For Marx, revolution is a natural result of the development of Capitalism, but Capitalism also dissolved history, and temporality, so the naturality of revolution must be immanent in every moment of its development: its like Walter Benjamin said, we must bring about a real catastrophe, as opposed to the constant "accidents" of human suffering under the system that come about with almost mechanical regularity.
In any case, I don't remember Marx ever being either an academic, or particularly hard to read in most cases, even if a thorough familiarity with German Idealism is a great help to understanding him more deeply. Even Foucault was technically an academic, but only because he helped organize a nearly successful revolutionary movement that managed to extract the concession of an entire university (Paris VIII) out of the government which he then ran, and is still being run by his students and colleagues to this day.