1. They were more violent.
Yes, they were violent, but no more violent than any other people at the time. It was an age of violence. In fact, the most violent regime to emerge from the the vacuum left behind by the Roman Empire were the Carolingians who conquered most of continental Europe with the intent to forcibly convert all pagan tribes to Christianity and to slaughter all who resisted. So effective were their campaigns that there wasn’t an army in the world who dared face them at the height of their power under Charlemagne, not even the Vikings. Not until the death of Charlemagne and the emergence of constant warring between his sons over inheritance did larger scale Viking raids begin in Carolingian lands (France/Germany/Poland).
2. They were christianized quickly.
The Christianization of Scandinavia did not occur overnight. The first monarch from any Scandinavian territory to convert was Harlad-Klak of Jutland who did so only to rally support from the Carolingians to help him in his claim to the throne of Denmark in around 815 A.D. Not until the mid 11th Century can we say that Christianity was prevalent among the Vikings, and pockets of paganism survived well into the medieval period (1066-1492).
3. They were one people.
When we use the word Viking we really do a disservice to the memory of Viking Age Scandinavians. It is a blanket term that is used to apply to anyone who lived and left Scandinavia (Denmark, Norway, Sweden) between the years 790 A.D. and 1066 A.D. They were not, however, as unified a group as we remember them today. The period immediately preceding the Viking Age was a time when settlements in Scandinavia were relatively isolated from one another, except for trade. These settlements had their own traditions, often owed allegiance to differing deities, and developed in parallel with, but separated from, other settlements. By the Viking Age, there were many groups who differed from one another tremendously. For example, a Norwegian from Vestfold may have differed as much from a Swede from Uppsala as he would have from a Saxon from Saxony. Yet today we make a stark distinction between Saxons and Vikings because the differences between them are generally recognized. Much like Scandinavia today, there were linguistic and cultural variations between the people of the region—differences which endure to this day.