The 20th century saw a number of German Jewish philosophers who were all deeply influenced by Husserl and Heidegger, but who all in one way or another followed paths opened up by Husserl's phenomenology and Heidegger's existentialism to non-phenomenological and non-existentialist destinations. They seemed to end up at something like a return to the ancients. Among these one might mention Hannah Arendt, Hans Jonas, Edith Stein, Leo Strauss, and Jacob Klein. Klein is certainly the least well known, but I think he is also the most profound and the greatest.
The essays in this collection show a great variety of subject-matter and approach, but they all show his profoundly philosophical way of thinking.