This has nothing to do with Germany that came after in 1871. The Prussians were evil without a doubt. They subdued the Poles and French without mercy. It was a very brutal empire. I can imagine them hating the Austrians as well. Very, very, very evil empire. Denmark was obviously extremely evil. Georgian England (George I and II, who were Lutherans) was also an evil era.
Yes the Prussian empire was brutal, but you have to remember that most of the empires that succeeeded during this time were brutal. It was the way of life back then. If you were not tough and brutal then someone who was tough and brutal was going to conquer you.
Prussia expanded sure, but it was only to unite Germany and nothing more, they did not take over any provinces not German, they simply succeeded in what Austria had wanted to do for hundreds of years. This is not brutal it is simply uniting a people that had not had the luxury of nations like Great Britain and France to be united. Even these conquests and unison weren't one hundred percent uniting as some states like Austria and Liechtenstein still existed indepandantly. As for how they treated citizens they weren't overly harsh and although they had serfdom for a time it wasn't near as bad as countries like Russia. To today's standards it would look bad but for back then it was average for a European nation. So in short no they were not brutal.
No, the Prussian Empire was not brutal, because it grew rapidly, in terms of the economy and the wealth of its people. Life was pretty good in the Prussian Empire, because they were strong militarily. King Wilhelm I might have gone beyond his authority a little bit in an attempt to increase the empire, but on the whole they were a fair government that paved the way for modern Europe.