Despite his negative assessment of Severus, sounds fairly sympathetic in the first para:

Distracted with the care, not of acquiring, but of preserving an empire, oppressed with age and infirmities, careless of fame, and satiated with power, all his prospects of life were closed. The desire of perpetuating the greatness of his family was the only remaining wish of his ambition and paternal tenderness.

Severus dies in Britain, leaving the empire divided between his two sons Caracalla and Geta, the former of whom kills the latter but does not last much longer himself, despite his aspiration to be a new Alexander the Great.

in no one action of his life did Caracalla express the faintest resemblance of the Macedonian hero, except in the murder of a great number of his own and of his father’s friends.

Macrinus takes power but doesn’t last long – is he the first emperor who doesn’t even make it to Rome in his reign? Gibbon seems to see him as a reformer but that appears to be code for “jumped-up bureaucrat”. Then we get Elagabalus, who introduces his own religion to Rome.

In a magnificent temple raised on the Palatine Mount, the sacrifices of the god of Elagabalus were celebrated with every circumstance of cost and solemnity. The richest wines, the most extraordinary victims, and the rarest aromatics, were profusely consumed on his altar. Around the altar a chorus of Syrian damsels performed their lascivious dances to the sound of barbarian music, whilst the gravest personages of the state and army, clothed in long Phoenician tunics, officiated in the meanest functions, with affected zeal and secret indignation.

I don’t know about the indignation, it sounds rather fun! Alas, Elagabalus turns out to be a Bad Emperor not so much because has sex with lots of women, which Gibbon doesn’t mind too much, but because he shags men as well. The end of his story is by now a familiar one. (Is he the second emperor to be killed by the Prætorian Guards?)

Gibbon is not a feminist.

In every age and country, the wiser, or at least the stronger, of the two sexes, has usurped the powers of the state, and confined the other to the cares and pleasures of domestic life. In hereditary monarchies, however, and especially in those of modern Europe, the gallant spirit of chivalry, and the law of succession, have accustomed us to allow a singular exception; and a woman is often acknowledged the absolute sovereign of a great kingdom, in which she would be deemed incapable of exercising the smallest employment; civil or military.

Indeed, what is striking is that after he condemns Mamæa just for being a woman, he goes on to explain just how good she was at running the empire through her son Alexander Antoninus.

The provinces, relieved from the oppressive taxes invented by Caracalla and his pretended son, flourished in peace and prosperity, under the administration of magistrates, who were convinced by experience, that to deserve the love of the subjects was their best and only method of obtaining the favour of their sovereign.

Much on Alexander’s efforts to reform the military, though I would have liked an assessment of how far he got. He also declared all free-born inhabitants to be citizens, which is surely worth more attention than Gibbon gives it.

Then a passage on the economics of the empire, which I found a bit lacking in substance; also I’m not an economist and the vocabulary here seems to have shifted quite a lot in the last 230 years. The explanation for the grant of universal citizenship is that it meant more money for the treasury; I really want to know more about the political currents leading up to it.