Michael Grant, The Twelve Caesars, (New York: Scribner, 1975), 31-33:

The gift which contributed most largely to [Caesar's] success was an abnormally energetic ability to get things done. This was conspicuously apparent in the occupation of warfare in which he excelled all his rivals. . . . The point was that he could do everything with extraordinary speed. . . . Caesar lived at a faster tempo than the people who had to contend with him, and this gave him an enormous advantage, offering the widest scope to that capacity for the unexpected, unpredictable action which his friends found such an irresistibly attractive feature of his talents. . . . In most of what he did—though not quite everything, as we shall see—clear vision of this kind was Caesar's outstanding characteristic: the product of exceptional brain-power guided by a will of steel. Even Cicero, when he saw Antony trying to step into the dead dictator's shoes, knew that the anti-climax was absurd. ‘Your ambition to reign, Antony, certainly deserves to be compared with Caesar's. But in not a single other respect are you entitled to the same comparison. . . . His character was an amalgamation of genius, method, memory, culture, thoroughness, intellect, and industry.’

Matthias Gelzer, Caesar: Politician and Statesman, trans. Peter Needham (Cambridge: Harvard university Press, 1968), 329-331:

Caesar, if anyone, deserves to be called a master of politics. He was equally great in understanding general political trends as in directing them. With consummate skill he handled the machinery of political details, without ever sacrificing his major aim of winning decisive power. . . . What a tragedy lies over the life of the greatest genius produced by Rome—to be snuffed out by Romans who imagined that they were acting on behalf of their res publica! His demonic genius raised him in every respect above all his contemporaries—through his spiritual and physical vigour, through the faster tempo of his life, through his free-ranging gaze which, unfettered by traditional concepts, everywhere discovered new possibilities, and through the masterful way in which he overcame difficulties and realized the most daring plans. Thus, although he was a Roman through and through and intended only to use his rule in order to raise the imperium populi Romani to the level of perfection required by the circumstances, nevertheless the flights of his genius lifted him to a lonely eminence where others were unable to follow him.

Zwi Yavetz, Julius Caesar and His Public Image, Aspects of Greek and Roman Life (Ithaca: Cornell University Press, 1983), 212-213:

To sum up, even those who reject the idea that Caesar tried to establish a monarchy and a divine cult must admit that he was much more than just a Roman dictator. They must also agree that his performance and achievements made restoration of the old Republic impossible once and for all. Whether all this was planned or brought about accidentally matters little. Celeritas [speed, swiftness] was distinctive of his style, impulsiveness led to his downfall. Many were enchanted by him, yet not a few felt repulsed. Since he neither wanted, nor could afford, to base his rule on a single class of society, he tried to curry favour with heterogeneous groups, at one and the same time. In his struggle for the support of the masses he overcame Pompey, but at the same time made considerable efforts to appease the nobilitas. He was called a benevolent ruler, but also a cruel despot. . . . He was on the whole a moderate statesman, who was nevertheless unable to avoid the impression that he put through his moderate policies by ruthless force. . . . Caesar did not have the gift of what the Romans called humanitas. Pliny the Younger defined it as the capacity to win the affections of lesser folk without impinging on greater (Ep. IX, 5). With his gifted intuition, Caesar ushered in a new epoch in Roman history. But he relied so much on his personal charm that he overlooked the need for tact, especially when he thought that he was in the right. Success lay open to a less brilliant and therefore more tolerant man [i.e., Augustus].