I was brought in by a staffing company. I completed one or two phone interviews with engineering not HR. I then completed a full day panel interview. All questions that were asked seemed very reasonably. You should be prepare to answer questions about your past experience and give examples etc. I had experience and interest in the core product area. Therefore it was not hard to show interest in product line. I think showing interest in product and willingness to learn and were key to getting the offer.