In the literature on Hegel, Hegel’s references to Spinoza are typically accepted at face value. Hegel was one of the all-time greats, but his treatment of Spinoza is a terrible injustice.
Pierre Macherey’s untranslated five-volume line-by-line commentary on the inferential structure of Spinoza’s Ethics is, I think, the best discussion of Spinoza in any language. A smaller work of Macherey, Spinoza or Hegel, has been translated to English, and develops many of the points I would wish to make.
I have my own issues with Spinoza. Among other things, he is unfair with Aristotle in much the same way Hegel is unfair with Spinoza. (In both cases, we are dealing with a high-handed and cavalier treatment from a great distance, and no substantive textual engagement.)
If we take a step back, we can see that modernity from the time of Descartes experienced what Kant would call antinomies (unresolvable dilemmas) with regard to questions of freedom and determinism. These, however, were not eternally given, but resulted from specific, contingent historical developments. These include not only emerging modern science but also some very specific features carried forward from medieval European theological controversies.
Since the early modern period, many philosophers have struggled to formulate their own incompatible ways of trying to assert both billiard-ball causality and a hyperstrong concept of personal identity to which something like voluntaristic free will was attributed. Even Kant and Hegel used a good deal of socially acceptable voluntaristic-sounding rhetoric that was at odds with their more careful arguments. (In a real world where audiences have prejudices, philosophers who want to be heard have to be careful to gauge their audience, and pick their battles wisely.)
In this context, Spinoza stands apart from the rest. Like the others, he wanted to assert modern-style univocal causality, but the kind of freedom of reason he argues for in Book V of the Ethics does not presuppose the hyper-strong personal identity and free will others wanted to assume. He also famously mounts a head-on critique of free will.
Ethically, Spinoza was profoundly committed to reason and an immanent understanding of nature and society. He published the first critical textual analysis of the Old Testament, and was among the first open advocates of free speech. His work was a major inspiration to the left wing of the Enlightenment that gave us the ideal of democracy.
Among philosophers, he also stands out for giving unprecedented attention to emotions and their interaction with reason. He is particularly concerned with the harmfulness of sad passions, and recommends that we use joyful passions as well as reason to help free ourselves from the grip of the sad passions.
Hegel complains that Spinoza dissolves the subject into the One, and things like that. We might say he should have paid more attention to Spinoza on the freedom of reason, but this might well have alienated important parts of Hegel’s audience.
Spinoza rejected the theologized Aristotle, and knew no other version. In spite of this, I think Aristotle would agree that Spinoza’s arguments against free will by no means rule out Aristotle’s moderate conception of deliberation and choice. The problem has been that many modern authors have felt it necessary to defend what are actually unnecessarily extreme versions of freedom. (See also Ends.)