The Romans did not consider every culture they faced that was not Roman barbarian. They considered the Celts and the Germans barbarians, but not the Greeks or the Persians. popular culture is in some ways right to portray Rome as they do. Also, this depends on the time period. By the late empire, the Germanic barbarians much more like the Romans. However, Rome was much more centralized, both in the time of the republic and in the Empire. The Romans were a more urban culture, certainly. They built stone cities, all planned in grids. They had running water, baths, central heating, paved roads, even fast food restaurants. They were considerably cleaner, at least in the republic and the high empire. Germans washed in rancid butter and fat. So, if the engineering skill of the Romans counts for anything, they were absolutely more civilized. It should also be noted that no written sources survive from antiquity in a Germanic or Celtic language. The first written sources we get are recorded in the middle ages. Caesar tells us that the Celts were familiar with the Greek alphabet and used it to write in their language, however. This was an uncommon practice, however. To my knowledge, no documents of this type have survived, meaning that the literacy rate was very low if there were a written language. If you would like to know more about these cultures, I would recommend Tacitus' Germania as well as Caesar's Gallic Wars. These two sources are likely to highlight the areas where the Romans find the Celts/Germans uncivilized. Additionally, I would recommend David Rankin's book "Celts in the Classical World". Rankin is useful because he sheds a more positive light on the Celts and will critique the classical authors. Hope this helps!