Roman portrait sculpture, especially in the later days of the republic, was very "verist", showing men very realistically, literally warts and all, with battle scars, and ugly features. Those "ugly" features were a testament to the truly Roman virtues of the person. It was not supposed to be a portrait of an idealized god-like figure, but rather someone showing those real-world traits that made an authentic, respected Roman citizen. So, in a sense, these "ugly features" were really showing an idealized image of a truly Roman man.

This was very different from the Greek inspired style of Roman sculpture that we see very often. Augustus, in his Prima Porta portrait, is shown as essentially a young Greek God in armor. That young portrait was not updated as the emperor aged, and it remained as a propaganda image of the emperor as a young, unchanging god. But that was not necessarily the sculptural style that is representative of Roman art. The look of Nero, and of countless lesser known and unknown Roman citizens in the marble busts that survived to this day, is more in line with the authentic Roman art of the late republic and early empire.

Source: P. Stewart, Roman Art, 2004.