The impressions that Europeans had of the Native Americans in what is now the United States were, of course, rather varied. Different Europeans had different opinions, as you might expect. The National Humanities Center link has a pdf with lots of accounts of what Europeans thought -- follow it to see some of them.
In general, there tended to be two schools of thought. Some Europeans thought that the Native Americans were "noble savages." They thought the Native Americans were sort of pure and unspoiled and closer to how people should be than the civilized Europeans were. Others, however, had very negative views of the Indians. They saw them as pagan savages who were very dangerous.
So there were many different reactions by Europeans to the Native Americans.