The decadence of Rome never looked so good. The movie traces the rise and fall of Caligula, the last real emperor of the united Roman Empire; before the military took over the government and instituted a line of puppet rulers.
Nothing is held back in showing the moral decay and decadence of the final days of the empire. Because of this, there are very few people who will not find at least some part of the movie offensive. While the attempt at realism is admirable, it makes it difficult for some viewers to look past the offense to their personal sensibilities and appreciate the film as a whole.
The movie has a lot of big names stars, but strangely it is a relative unknown, Theresa Ann Savoy, as Caligula's sister that provides the best performance. Malcom McDowell, John Gielguld, and Peter O'Toole present performances that are fine, but far from their best.
The film does seem to lack anything resembling a plot. Instead of a cohesive story, the characters move from one unrelated scene to the next. The movie is more akin to a voyeuristic view into Roman life as it was during this period of time.
The sets and the atmosphere, however, are excellent. "Caligula" presents the best vision of the opulence and decadence of Rome since Fellini's Satyricon. While some viewers have criticised the movie as exaggerating the concept of Roman orgies, one should remember that "Caligula" takes place during the fall of Rome, where the power of the Emperor and nobility had reached the epitome of corruption. The days when Rome was a center of scientific and philosophical advancement had long disappeared by the time Caligula comes to power. During this time intellectuals and dissidents were slaughtered, the nobility had given up any appearance of proprietary, apathy ran through the citizenry like a plague, the military assumed more and more power, and celebrations and orgies were held constantly in a vain attempt to stave off rebellion. Because the strength of the movie is in its ostentatious depiction, I suggest watching the long version (the short version just doesn't convey the intended vision strongly enough).
While not everybody can appreciate the movie, I would recommend it to any student of Roman history or afficionado of film techniques.