As a disclaimer, I'm a civilian reapplicant so I've had 4 interviewers to date.
The single most important question is "Why medicine, and why in particular military medicine?" or some variation of that. All four of my interviewers asked that. Three of my interviewers asked me about leadership ("Tell me about your most important/humbling leadership experience") and three of them also asked me about where I saw myself in the future ("... outside of, you know, medical specialties.").
The other question that all four interviewers asked me was "Do you have any questions?".
Aside from that, three of my four interviews were very conversational (almost too conversational, which can throw you off). The fourth interview was similar to a traditional "drill you with interview questions" interview but the Q/A session at the end was very conversational and casual. I talked about things like martial arts or research or rocket launchers or therapy pets (Shetland!) with my interviewers.
You generally won't get oddball questions ("What is your favorite microbe?") unless it's very specific to you (i.e. if you're passionate about microbiology).
Other interview questions that I encountered (mostly from that one interviewer):
-Why our school?
-What do you offer us?
-How would your friends describe you?
-What is the last book that you read?
-Tell me about your most significant research experience
-Tell me about the time you spent abroad (because I did medical volunteering abroad)
-What would you say is the biggest downside of military medicine and how do you plan on overcoming that?
-What military exposure do you have outside of your work with ROTC and veterans?