Obviously the reformist theologians of 16th century Germany had a bone to pick with the Catholic Church to a greater or lesser extent. But do any of them comment on Orthodox christianity, whether Greek or Russian? How aware were they of their practices, beliefs, and traditions, and did they see them in the same light as the Catholic Church, in a favourable light, or somewhere in between?
Indeed there was a lot of interest for the orthodox churches by the reformators that built the protestant churches. Notably in the Dispute of Leipzig[1], Luther pointed out to his opponent Johannes Eck the fact that Rome had not been able to win supremacy over the Greek orthodox church and thus that the Pope had no divine mandate over all Christians. Luther realized that he had his opposition against a centralized church and the goal of an organization like in the first millennium in common with the orthodox churches.
Unsurprisingly, this soon led to close exchanges between the Protestant and Orthodox churches, as in the letters between Melanchton[2] and the Joasaph II, Patriarch of Constantinople, or between Lutheran theologians in Tübingen and Joasaph's successor Jeremiah II[3].
That does not mean that Lutherans ignored major differences between protestantism one the one side and roman-catholicism together with the orthodox churches on the other: its stressing on Individualism and the differences in rites. These differences soon led to both Protestant as well as Orthodox churches starting to try and proselytize each other's members and eventually kill the dialogue until renewed efforts in the 20th century.
Sources
[1] Mattox, Mickey; Serina; Richard; Mumme Jonathan (Eds). Luther at Leipzig: Martin Luther, the Leipzig Debate, and the Sixteenth-Century Reformations. Leiden and Boston, Brill, 2019 - ISBN 9789004414624.
[2] Asproulis, Nikolaos. The Encounter between Eastern Orthodoxy and Lutheranism: A Historical and Theological Assessment. The Ecumenical Review 69.2, 2017, p215ff.
[3] Hämmerle, Eugen. Tübingen und Konstantinopel: der Briefwechsel zwischen dem Ökumenischen Patriarchen Jeremias II und den Tübinger Theologen 1573-1581. In: Blätter für württembergische Kirchengeschichte 83/84, 1983, p201ff.