I'm listening to The Commentaries of Julius Caesar on audio right now. Some thoughts on the book:
1. This is the second time I've gone through the book, and it's much more understandable. The book is hard to fully grasp without background.
Caesar is an immensely clear writer, but there's 10,000 things left unsaid in his book. If you don't understand the background of his life, and the general scope and plan he had -- and the general machinations of Roman society -- then a lot of actions don't make as much sense.
I've gone through enough Roman history now that I understand the backstory about how Roman politics and military works -- tribunes, consuls, governors, the immunity to prosecution while in office yet retroactive liability to prosecution after leaving office, how the various Popularii leaders had been executed or murdered, how indebted most of the aristocratic politicians became to run for office, the state of the equestrian class, troop makeup, etc.
To really get the most out of the book, you need to know something of the political and financial situation of Caesar, his men, and their general political party. It's a good read without that, but a fantastic read with it.