The Empire is an elitist society ruled by the sith who are, in essence, evil. Were their no sith ruling the Empire, they would probably become much more lenient.
On to the main question, yes, I believe the empire to be evil. Their are a select few imperials who are actually good men and women, Problem being, the sith are in power and are brain washing each generation of the empire and instilling fear in those who hold different opinions; the empire, because of the sith, is a tyranny. To put it in perspective, the Empire is like the Soviet Union, or Iran.
Despite this I role an Marauder as my main because I enjoy playing the marauder and its armor I get.