DL (no, I was not familiar with him either) apparently has been much ridiculed by later philosophers for his writing skills and choices. Holt starts:
Poor Diogenes Laertius. He gets no respect. A “perfect ass”—“asinus germanus”—one nineteenth-century scholar called him. “Dim-witted,” said Nietzsche. An “ignoramus,” declared the twentieth-century classicist Werner Jaeger. In his lyric moods he wrote “perhaps the worst verses ever published,” an anthologist pronounced. And he had “no talent for philosophical exposition,” declares The Oxford Companion to Philosophy.
His style of biography is summarised this way:
In all, over eighty individual figures get entries—including one apparently rather clever “lady-philosopher,” Hipparchia the Cynic. (A couple of female students of Plato are also mentioned, one of whom is reported “to have worn men’s clothes.”) The author typically says something about the philosopher’s family origins and his teachers, then moves on to anecdotes about his life and apothegms expressing his opinions. We are furnished with details of his sex life, the more scandalous the better. Letters (some spurious) and wills are quoted, and the philosopher’s written works are listed. These stacks of titles, sometimes extending over several pages, are extremely valuable, since the works in question (like the aforementioned dialogues of Aristotle) have generally vanished. Finally, we are given an account, or several alternative accounts, of the philosopher’s death, often with an ironizing comment by the author in what he calls “my own playful verses.”Holt then explains that Hegel and the philosopher I love to malign, Nietzsche, disagreed about the matter of the importance of how philosophers live their lives:
The principle of selection for these biographical materials is simple: cram in everything, without regard to plausibility or philosophical relevance. Physical details are abundant, if not always consistent. We are told of Zeno the Stoic, for example, that “he was lean, longish, and swarthy,” but also that he was “thick-legged, flabby, and weak”; also that “he delighted…in green figs and sunbathing.” Plato is “weak-voiced” but mocked for his “long-windedness.” Aristotle had thin calves and small eyes, wore fine clothes and lots of rings, and “spoke with a lisp.”
In his Lectures on the History of Philosophy, Hegel judged the work of Diogenes Laertius harshly. “A philosophic spirit cannot be ascribed to it,” he declared; “it rambles about amongst bad anecdotes extraneous to the matter in hand.” What is important, Hegel argued, is not that a philosopher lived in such-and-such a way and said this or that; rather, it is how the philosopher fits into the evolution of human consciousness toward truth.That's probably enough cutting and pasting, go read it all.
After Hegel, the reputation of Diogenes Laertius suffered a sharp decline among both classicists and historians of philosophy—as witness the abusive quotations I opened with. Yet one abuser, Nietzsche, later turned into a passionate (if ambivalent) defender. As a philologist, Nietzsche had contempt for the sloppy scholarship that went into Lives. But as a philosophical subversive, he had two motives for championing the work. The first was his hatred of Socrates’s moral optimism—a precursor, he thought, to slavish Christian morality—and his preference for what he saw as the darkly “tragic” worldview of the pre-Socratics. From the materials that Diogenes Laertius had preserved on figures like haughty Heraclitus and Etna-leaping Empedocles, Nietzsche hoped to recapture a sense of pre-Socratic tragic grandeur in Greek culture. His second motive for championing Lives was a more general one. Whereas Hegel insisted that the biography of a philosopher was irrelevant to his conceptual contribution, Nietzsche took the opposite view: bios is the ultimate test of logos. He wrote:
The only critique of a philosophy that is possible and that proves anything, namely trying to see whether one can live in accordance with it, has never been taught at universities; all that has ever been taught is a critique of words by means of other words.Now, one is loath to put oneself in the position of adjudicating between Hegel and Nietzsche. In this case, however, I think it is safe to render a verdict, if a disappointingly bland one: they are both partly right.