Do not use this time to judge the opportunity. Use this time to sell yourself. Focus on providing good answers to the interviewer's questions and asking good questions of them. Evaluate the opportunity a few hours after you have left and have had a chance to digest the experience.
If this were a slow dance, the interviewer should lead. Let the interviewer drive the process. Do things like ask if it is okay to take notes, or take a pause before answering a question to make sure that the interviewer has finished asking the question (and to give yourself a moment to think before you respond).
While you should not use this time to evaluate the opportunity, it is advisable to ask a handful of questions that will provide you with information for when you are later deciding if this is the right move for you. Ask good questions. If you do not ask any questions it may make the interviewer think that you don't care.
Most of your compatibility with the company and the role is determined by how you look and how you sound. Try to make your answers concise. Make sure that you are actually answering the interviewer's questions instead of going off on a tangent about something else. Dress appropriately for the interview. This may mean something different depending on your geographical location. For example, appropriate dress for East Cost interviews is usually business formal, while appropriate dress for West Coast interviews is often more casual. Ask you recruiter if you are uncertain of how formal the setting will be.
Enthusiasm may separate you from the rest of the talent pool. Some say that you are judged during the first two minutes of an interview, while others say that it is the first ten minutes. In either case, enthusiasm about the role and the company always makes for a good impression.
Last but not least, don't panic! Don't be so nervous that you are robotic. The interviewer wants to get to know you and to have a real conversation with you. Any interviewer who has been properly trained will sense if you are just telling them what you think they want to hear. Always be honest, but remember not to say anything
Yes, I intentionally left off any mention of having a strong handshake. A strong handshake will do you no good if you show up in a wrinkled shirt and spend your time talking over the interviewer. While it is a good way to start things off, a strong handshake is highly overrated.