There's this odd perception that Caesar is somehow less credible historically than our other sources, and I don't really know why. I can only assume that it's from kids taking high school Latin (since the de bello gallico is always the text mentioned when in fact the de bello civili is by far more rhetorical and problematic), but I find it very odd. In point of fact Caesar is, along with Cicero, among the most important historical sources for the late Republic. Like Cicero, Caesar was a contemporary of the events which he discusses, which is exceedingly rare in antiquity (the next-closest major source we get for the period is Sallust, who doesn't count because the only "contemporary" event in his surviving texts is the Catilinarian conspiracy, which took place when he was only 23). Moreover, though Caesar employed rhetorical devices and wrote for political purposes^^1 he employed the Plain Style and wrote in such incredible detail that he is totally unmatched--compare Caesar to some of the speeches of Cicero on which we rely (quite heavily) and anyone with any understanding of rhetoric at all will see how really quite straightforward Caesar is. Caesar's thoroughness is worthy of particular note, since the alternatives of Caesar would be Plutarch, Suetonius, and Appian (I guess Cassius Dio too, but I have difficulty keeping a straight face when I read "an actual historian like Cassius Dio"). One look at them will show how much more detailed Caesar is. He gives detailed, frequently day-by-day, reports on his actions, which would be easily fact-checked (particularly if these are edited transcripts of his litterae). Any "spin" in Caesar is not to be found in his record of events, those are considered pretty impeccable, but in his rhetoric (such as it exists), particularly in his interpretation of the significance of events. Such reasoning is actually relatively unusual in the de bello gallico, you really only see it in a handful of places (the initial incursion into Gaul, his invasion into Germania, the reasons behind his expedition into Britain, and maybe Gergovia). It's vastly more prominent in the de bello civili, in which he is at pains to point out whenever possibly why he's in the right--but most high school students have never read the de bello civili in Latin, because it's much more involved as a piece of literature.

All historical sources have bias, and all ancient sources in particular are notoriously flawed for all kinds of reasons. This is a fact of historiography, and one that should not be used to point the finger at this or that ancient author in order to dismiss him--especially not an author as important as Caesar! Because here's the thing, problematic as Caesar is he is without doubt one of our best historical sources, and among our most trustworthy. He is certainly without question the single best military author we have in Latin, there is simply no way to debate that point. And really Caesar is actually pretty honest. He portrays the "fog of war" (and is one of only a handful of ancient authors who acknowledge the concept that warfare is confusing) and is very ready to admit when he makes a mistake--he rationalizes his mistake, saying why he was misled or what went wrong, but he admits it up front (with the possible exception of the German expedition). The weird singling-out of Caesar is a feature, as far as I can tell, of high school students and early undergrads who don't have very much experience with actual Latin texts--a little reading and it's pretty clear that Caesar's really quite good.

1: The precise purpose of the de bello gallico and the de bello civili is unknown. Both other users have noted that they're not history proper, and that's about all we know. Commentarii were originally transcripts of the acta of, for instance, the collegium pontificum. By Caesar's time they had come to refer also to drafts of orally-delivered addresses, and from this it's been suggested that the de bello gallico was an edited publication of Caesar's dispatches to the senate, the litterae which provincial magistrates were supposed to send (though literally nothing happened if they didn't). These would have been read aloud (hence the third person persona) by an agent, and the suggestion seems plausible but we cannot know for sure. How they came to be collected and published, however, is even more unknown. At the very least we can say that they were not compiled directly, but clearly edited. Nor do we know the intended audience of the final publication, so babbling about Caesar's political bias is silly--we don't know what perspective Caesar was trying to portray and for whom

De Bello Gallico and Bellum Civile are not works of history and therefore should not be judged as works of history. They are primary sources.

Those books are first-hand accounts written by what was arguably the second most famous military commander in human history. Yes of course he was writing to impress his contemporaries and yes he downplayed or avoided mentioning his defeats and setbacks, and took more personal credit occasionally than he maybe deserved. And he described his opponents and allies and troops in ways that played to the preconceptions of his intended audience.

That doesn't mean we don't take him seriously. We compare his account to the work by an actual historian like Cassius Dio, and archaeologists try to connect dig sites to events and locations he described.

Just because you don't take a primary source at face value with absolute credulity doesn't mean you don't take it seriously.

And it also doesn't mean you can't enjoy reading it. Too many undergrad and grad students get a little snobbish about being too hyper critical of sources and histories, and forget why we all were drawn to this field in the first place. De Bello Gallico and Anabasis are what made me fall in love with history.

Don't let your friends' attitudes affect your enjoyment of Caesar. Be aware of the context and know that you're reading a very clever piece of political propaganda, but allow yourself to enjoy it.