I am a PhD student in Germany (physics) and I will have my PhD defense in some months. I am not German. My thesis is mainly based on two Physical Review Letters and a paper not yet published (submitted to Physical Review B). The reviews (Gutachten) on my thesis are positive: I've got 1.3 and 1.7 (1 is very good, 4 is sufficient). The defense will consist of an oral presentation of my thesis and of an oral exam (Rigorosum) in the presence of two professors (two main topics, one of which is completely unrelated to my thesis).
My question is, how important are the presentation, the rigorosum, and the reviews, respectively, for the decision of the final grade? Is it possible to fail the PhD defense, having good reviews? Actually, I am mainly concerned about nasty questions after the thesis presentation and during the Rigorosum...