Plotinus, IIRC, believes that Luther was more successful not merely because of the printing press, but because his theology was significant more solid and appealing than that of previous men who disagreed with Rome.
I would have to let Plotinus defend that thesis himself, but it's unconvincing to me. At its core, Lutheranism suffers from basically the same errors as the heretics that preceded him; and then when you fine-comb his beliefs, there's nothing of substance. It's mostly a lot of political flip-flopping (such as his brief endorsement of polygamy), rabble-rousing ultra-antisemitism, and a lot of weird one-shot stuff that you might come across in the
Tischreden.
I really have to attribute the widespreading of Lutheranism to a really good PR campaign and contemporary politics. His earliest allies were not theological zealots or devout reformists; they were German princes that were investigating if they could use a demagogue like Luther to spite Kaiser Karl V. The news of Luther's condemnation in
Exsurge Domine came out only a week after the Papal condemnation of another German populist author (name escapes me)*, so the initial traction that Luther got from the theses was largely an overlap with a general perception of Italian preferentialism in the Catholic Church (primarily the reason why Erasmus initially sympathized with Luther but backed away as Luther's theological insanity became more and more apparent).
EDIT: The controversy between Ulrich von Hutten and Franz von Sickingen against the German scholar of Hebrew manuscripts, Johann Reuchlin, is what I was thinking of. The
Epistolæ Obscurorum Virorum case had been settled in virtually the same week as Luther's condemnation, so the Germans outraged over Reuchlin's manifested injustice spilled over into defending Luther, allegedly then a poor German monk being wronged by Rome just like Reuchlin was. The contingent events that coincided with the Protestant Reformation are so often forgotten, but so important in the outcome.
@light spectra: Peter Waldo of the Waldensians
I actually had to look this up, because the name given to this person when I studied it was Petrus Valdes. Unnecessary anglicizations aside, yes, they were a heretical sect. Although they appear to be a protofranciscan organization at first glance, Valdes was (according to all information available about him) quite dead-set on denying the apostolic authority of the Catholic Church and the Sacrament of Holy Orders.