While doing some research on Luther as a favor to a friend, I came across the Roman Catholic site "New Advent" (of which many are already aware), and I found this interesting passage (below) in its entry on Martin Luther.
The part I bolded, I think, is actually a fair articulation of Lutheranism (though not complete, of course). Read the whole entry if you want a good headache.
Or, for a completely Christ-less treatment of their diagnosis of Luther (and a total migraine) read the entry on scrupulosity.
Of course this self-willed positiveness and hypochondriac asceticism, as usually happens in cases of morbidly scrupulous natures, found no relief in the sacraments. His general confessions at Erfurt and Rome did not touch the root of the evil. His whole being was wrought up to such an acute tension that he actually regretted his parents were not dead, that he might avail himself of the facilities Rome afforded to save them from purgatory. For religion's sake he was ready to become "the most brutal murderer", "to kill all who even by syllable refused submission to the pope" (Sämmtliche Werke, XXXX, Erlangen, 284). Such a tense and neurotic physical condition demanded a reaction, and, as frequently occurs in analogous cases, it went to the diametric extreme. The undue importance he had placed on his own strength in the spiritual process of justification, he now peremptorily and completely rejected. He convinced himself that man, as a consequence of original sin, was totally depraved, destitute of free will, that all works, even though directed towards the good, were nothing more than an outgrowth of his corrupted will, and in the judgments of God in reality mortal sins. Man can be saved by faith alone. Our faith in Christ makes His merits our possession, envelops us in the garb of righteousness, which our guilt and sinfulness hide, and supplies in abundance every defect of human righteousness. "Be a sinner and sin on bravely, but have stronger faith and rejoice in Christ, who is the victor of sin, death, and the world. Do not for a moment imagine that this life is the abiding place of justice: sin must be committed. To you it ought to be sufficient that you acknowledge the Lamb that takes away the sins of the world, the sin cannot tear you away from him, even though you commit adultery a hundred times a day and commit as many murders" (Enders, "Briefwechsel", III, 208). The new doctrine of justification by faith, now in its inchoate stage, gradually developed, and was finally fixed by Luther as one of the central doctrines of Christianity. The epoch-making event connected with the publication of the papal Bull of Indulgences in Germany, which was that of Julius II renewed in adaptable form by Leo X, to raise funds for the construction of St. Peter's Church in Rome, brought his spiritual difficulties to a crisis.