I had a similar experience at my interview. I had Dr. Lefebvre, Dr. Spier, and Dr. Hart on my panel. Dr. Spier was very nice and easy to read, the others were harder to read (but still nice). Dr. Hart asked a lot of open-ended questions, "give us your thoughts on..." type ones. I didn't really get any questions that I wasn't expecting or hadn't prepared for, and it definitely was nowhere near a grill session. My interview was fairly short as well, I think 25 min. or so. It definitely could've gone better on my part, for some reason I'm never able to speak coherently about my research, no matter how much I've prepared! 😛 Most of my questions were from my application, with a couple of ethical ones thrown in as well.
I'd like to point out, though, that even if you feel you got grilled, it doesn't necessarily mean anything. A lot of my bf's classmates were talking about their interview experiences after he told them about mine, and there were a variety of situations: some people thought they were grilled, others thought they were given easy questions.