I’m also a fan of the Colleen McCullough books, but she’s far better with Marius and Sulla than she is with Caesar, for the reasons that Sane Max mentions. Too many passages in which the great man’s toga barely conceals what lies beneath, etc, and the apologies are way OTT.
I would disagree with the opinion here of Caesar being a bad egg, however. He wasn’t out there proscribing people like various other luminaries before and after did, and he tried to work within the constitution as much as he could. That the system was already broken was not his fault, and the sheer bloodymindedness of those opposing necessary reforms and denying him due credit as a statesman, successful general and man of good family must have been very trying. His clemency was famous and, I think, genuine. Compare Caesar to Augustus and you see a lion and a snake, though the snake seems to get better press.
But back to the OP: as much as I love reading fiction about Caesar, I think it’s very hard to better his own words. Having copies of the Gallic War and the Civil War around the house is to my mind essential, and his battle descriptions are a constant inspiration as a wargamer.