All good interviewing is done this way. The goal of the interview is to get into the thought process of the interviewee. You just need them to give you a thread to start pulling.
I think a lot of candidates think they're immediately screwed if they don't have a compelling answer to every question. It's not seen that way on the other side of the table, at least not when I'm there. Often the interviewer himself is just trying to find a foothold that he can take to really start digging into something. Good interviewers throw out a bunch of questions that are designed to get you talking until you start talking about something they can sink their teeth into. Bad interviewers have no idea what to do and throw out stupid, random questions that sound like job interview questions to them, accept your answer, and then do it again for the entirety of the 30-60 minutes. At the end of your interview, they'll make the same decision they would've made if they'd only seen your picture and were told they had to decide from that (unless you managed to offend the interviewer during your responses ;) ).
Any nervousness I had as a candidate was permanently resolved after I started interviewing people and seeing how others reacted to interviews. Most interviewers are not disqualifying you for all the stupid crap you imagine. If you're good and they pass, they're either that incompetent in which case you don't want to work for them anyway, or they have many good candidates and the choice is then based on unknowable differences in perception like perceived likeability or other superficialities.