Caligula - grossly misrepresented. Possible incestuous relationship with his sister. Threatened to make his horse a senator to illustrate what a bunch of jokers the current lot were.
Nero - allegedly kicked his pregnant wife to death. Nice chap.
Good for the blood, guts and casual psychopathy. One of the more interesting characters, but out of a more terrifying place than say Messalina, Claudius' wife.
You've got to admire Vespasian, though. Stabilised the Empire after the year of four emperors, founded the next dynasty and provided a role model of good governance that subsequent emperors adhered to until that tit Commodus.