I think there is some truth to the fact that it is difficult to speak of all Protestants in one breath. However, I think there are some generalizations that may apply to most Protestants, in my opinion. First, they are based on Sola Scripture (the Bible Alone), along with personal interpretation of Scripture. Second, rejection of Sacred Tradition, which are the oral teachings of Christ, carried forth for these 2000 years. Third, rejection of authority of the Church which Christ founded. Fourth, recognition, to some degree, of Sola Fide (we are saved by faith alone).
But one could make the case that today, Protestantism has become so diffused that one can find almost any belief imaginable within some denomination if one just looks hard enough.