I was raised Lutheran so I am fairly familiar with Luther and his teachings.
While I don't think he was heaven-sent, I do think he did the Lord's work in bringing Christians back to Biblical teachings, and I do think for much of his life he was a faithful servant of God and Christ.
That said, I find the anti-Semitic ramblings of his last days to be troubling, but possibly explainable by his frustration at being unable to convert Jews to Christianity and possibly by an onset of senility, brought on by old age, fatigue, and said frustration.
Luther believed that non-Christians were lost. I am not as certain as he was that they are. I also disagree with his teachings on infant baptism.
Luther was not always an anti-Semite. Through much of his ministry he wanted to bring all people, including Jews, to Christ. The unwillingness of Jews to embrace Christ was a source of angst to him and he never got over it.