I will concentrate on the movie's historical accuracy (or its lack of it), since the previous reviews seem to either have overlooked it, or claimed that it is "historically accurate", or on the opposite extreme, that it totally ignored history.
"Caligula" does have some merit from the historical point of view, surely already present in Gore Vidal's original script. It's also very weak in many points.
The bare events of Caligula's life and reign are actually quite accurate. It may surprise many viewers that most of the secondary characters - Emperor Tiberius, Senator Nerva, the praetorian prefect Macro, Tiberius's grandson and Caligula's rival for the succession Gemellus, Caesonia, Chaerea (who murdered Caligula), his sister Drusilla - were all historical and, as far as the facts have come down to us, their portrayal in "Caligula" was fairly accurate, at least according to some ancient authors.
Tiberius did retire to the island of Capri in his last years and did invite the elderly Nerva to join him there, and ancient authors do claim that he indulged in sexual perversions there. Nerva really committed suicide as shown in the movie.
The conversations between Caligula, Nerva and Tiberius, probably by Vidal, really reflect contemporary views and issues - for instance, the deification of Julius Caesar and Augustus, Tiberius's predecessors: Tiberius was totally cynical about the whole thing, whereas Caligula firmly believed it. Throughout the movie, many of Caligula's lines come straight from ancient authors.
On the other hand, Nerva's comment on Caligula's "gift for logic" seems to owe more to Camus than to ancient sources - still, a nice touch, I thought.
Tiberius's murder by Caligula and Macro, Caligula's removal of Macro and Gemellus, his incestuous relationship with Drusilla, her death, his marriage to Caesonia, her giving him a daughter, his increasing tyranny, his farcical invasion of Germany and attempted invasion of Britain, and his murder by his own guard - are all historical facts, and on the whole not too inaccurately shown in the movie.
On the other hand, the movie's biggest weaknesses from the historical point of view are (1) the way it *looks* and (2) the suggestion that Caligula's and Tiberius's depravity were somehow "normal", part of Rome's "decadence".
The sets and clothes all look more like something from a Fellini film than from ancient Rome. Tiberius's palace on Capri is perhaps the most unrealistic, along with that ship, and the execution machine - and countless details.
The clothes aren't very realistic, either. Romans were more casual about nudity than we are today, and I suppose that their clothes might reveal much some times. But I doubt that Roman ladies would be as casual about parading half-naked as portrayed in the movie (I mean in normal situations, not the sex scenes).
Moreover, it's simply not true that "orgies" such as that portrayed in the movie were common among the Roman upper classes. Actually adultery - also on the part of males - was an offense punishable by death, at least for the upper classes (this didn't cover prostitution). The vast majority of the Roman senatorial class would, and did, find behavior such as that of Tiberius and Caligula scandalous.
However, Caligula's in cognito wanderings through Rome after Drusilla's death give perhaps for the first time in a movie a good impression of what ancient Rome actually was at night - dangerous, dark, chaotic, where no person of means would venture without an armed escort.
I also enjoyed the glimpse of what an emperor's routine largely consisted of, with Tiberius and Caligula stamping their seal onto endless piles of official documents.
"Caligula" was obviously intended to be mainly a pornographic movie - Bob Guccione made sure of that. But it also, at some point, was intended to have a core of historical accuracy, which is why Gore Vidal was asked to write the script.
This core is still present in the movie, and it's not true that you don't learn anything of Roman history by watching it.
But of course, I know that that's not what most people will watch it for. So perhaps Guccione was right.
