I have a tendency to react somewhat strongly whenever Heidegger is mentioned. Anyone participating as I do in a philosophy forum is likely to encounter his name with some frequency. Almost as frequently as his name is mentioned, I strongly react (I've managed to control myself now and then). This has been noticed. Recently, I was challenged to explain my reactions. This is an effort, or the start of an effort, to do so.
As may be guessed my reactions, such as they have been on that forum, have been adverse. They have been strongly adverse. I have a tendency to dwell on his Nazi past. In all honesty, I've condemned him as loathsome, an anti-Semite, a worshipper of Hitler, a despicable Nazi toady, a cruel and incessant enforcer of racial exclusion laws while rector at Freiburg, a twisted romantic, an ungrateful friend. And I maintain he was all of these things! I think he would have been happy to take the place of Goebbels if he could have, or at least would have delighted in being the chief philosopher of the Nazi Way. But, sadly for him, his considerable efforts to endear himself to Hitler failed, and he was reduced to pouting, for the most part, during the balance of his Fuhrer's reign. Unrequited love eventually silenced his praises for the man he called the present and future of Germany, and its law. But he never seemed to get around to condemning Hitler or the Nazis, except in commenting that they just didn't go about things the right way.
Well, you see what happens.
I've been told that the fact he was a Nazi has nothing to do with his philosophy or his influence, which are claimed to be profound. There's no doubting his influence, of course. I have my doubts about his philosophy. But, I don't hate him for his philosophy, except to the extent it led him to act as he did. I hate him for the man he was, and deplore the fact that a philosopher was--and could be--such a man. Think of it; a philosopher not merely buying into Nazi doctrines, but enthusiastically spouting them--indeed, justifying them. And, worse yet, implementing them.
It may be that I have too romantic or idealized a view of philosophy and philosophers. In any case, I personally can't think of Heidegger the man as someone separate and distinct from Heidegger the philosopher. And, I rather doubt he would make such a distinction.
My attitude towards Heidegger the man probably impacts my view of him as a philosopher. We tend to be dismissive of the intelligence of those we hate. But, I'll try to relate some of my problems with philosopher Heidegger without indulging in comments about Heidegger the contemptible man (oops! Sorry).
I must confess immediately that I can't stand reading him. Nor do I enjoy reading such as Sartre, or Kierkegaard, or Schopenhauer (most of the time), or Foucault, or Hegel, or Nietzsche (most of the time). I grow impatient. I dislike the terminology (especially the many usages of the word "being"). I'm American, you see, and we know what Heidegger thought of Americans--I'm probably incapable of appreciating the finer and more significant aspects of life, and am technology mad and money-grubbing (actually, I'm rather lame when it comes to technology).
Also, I find his fear of science and technology to be disquieting. There's something of the romantic and even mystic in Heidegger, I think, but it is a bad sort of romanticism that he seemed to glorify, and not just when it comes to the mystical destiny of Germany. We can't return to gamboling about the forests, if we ever did so (I suspect we didn't much). There can be no question that we can (and have) posed a danger to our environment, and there are dangers we must avoid. But, we will continue to manipulate the environment, and we will continue to employ science and technology to achieve our desires, and we won't do so because of a mistaken conception of metaphysics. That's what we do, and it will not change. We must learn to do so intelligently. I don't think Heidegger believed this is possible. In any case, I don't think he showed us how to do so in any useful sense. And I'm big on useful--but so of course was Dewey, and Heidegger hated him as representative of "Americanism."