This is what I learned when interviewing another person. A Good Interviewer is:
1. Able to take control of the interview, and knows where he or she is going with it (ex. In some cases, it might be much easier to make up the questions right on the spot (during the interview), rather then coming up with the questions before hand).
2. Is flexible. (ex. Able to adjust to the tone of the interview.)
3. Knows his or her limits. (ex. There is only so far you can go with an interview. This is best to keep in mind if when your going too far, or when your not even close to hitting the bulls eye. Don't ask questions that he or she will hate you for, but keep the respect).