Well if the vikings had never managed to cripple the native Anglo-Saxon kingdoms and gain a proper foothold, of course the later taking of Irland and Alba would never occur. The Wars in Irland in particular played an important role in the development of the Norse political tanistry-meritocracy system of government. If the Norse had never spread out so far either, the numerous intra-Norse civil wars during this time would never have occurred as the disparate kingdoms fought for dominance. While these civil wars significantly damaged the Norse population and kingdoms, arguably preventing a greater degree of viking conquest,they were essential in the development of more reliable central leadership to prevent the almost regular conflicts over leadership among the Norse.
As for ethnic differences. Just as someone mentioned about Kievan Rus, northern Francia would not have received the great influx of Anglo-Saxon refugees fleeing the vikings as they did. That would significantly alter the culture and genetics of Brittany and Angala (OTL Normandy). Spain is a real toss-up since so many forces were fighting for dominance, and the later addition of Norse mercenaries looking for loot, thralls, and land to settle only added to the chaos. The brief Varangian Guard created by Emperor Basil II would have lasted longer if Norse warriors didn't decide they had just as much opportunities fighting to ensure Norse dominance in Britain as in Constantinople. That might have prevented the proxy wars by both peoples for influence and control over Kievan Rus, likely sparing that country a lot of turmoil and conflict.
A major difference would be the loss in naval influence in Western Europe. Weaker vikings meant the other nations wouldn't have eventually been forced to try and develop more complete navies, thus the Norse wouldn't have ever been forced to adapt to out-compete them. The Age of the Sail would be unrecognizable without the viking naval culture permeating so many areas and kick-starting it.