I think those open-ended questions are great. It really gives you a chance to shine and show yourself. Remember, being a physician is more than just having good grades, able to memorize volumes of encyclopedias, etc. Being a good physician require you to be able to communicate, even in time of stress. Those open-ended questions are for them to see how well you can speak freely instead of asking a yes/no or a definite answer. Being in the hospital, you'll have to talk to patients you've just met, patients who are angry at you, patients who won't understand you, etc.
You should use those open-questions wisely and talk about yourself and NOT JUST SCHOOL. How I like to answer is that I ask them if they would like to know about my personal life, academic life, or both. Most of the time, they would want to hear both so I always start w/ my personal life. I tell them what I like to do, clubs i've joined in college, which college I went to, my hobbies, my family. By doing that.. you are able to carry out a conversation instead of listing... I got a 4.0 in organic chem, president of this club, etc.
After your personal life, you can talk about your academic life, taking classes, how you liked the classes, classes you disliked, etc. classes you wished you could have studied more for.
Remember... be personal with yourself. If you talk w/ emotion about yourself.. the interviewer will be able to tell that you are capable of speaking with emotions to others. Don't stare away, use both eye contact AND body language. Smile, laugh if you reminesce about something funny and TRY TO RELATE TO THE INTERVIEWER!!!! i.e. You can't talk about how good it is to have a pet and go on forever about it if your interviewer never had one.
Finally... Goodluck!