I've discussed this topic with many people since joining Zity: what exactly is it about med-fet that you find fulfilling and/or exciting? It's definitely not the same for everyone. I have enjoyed reading some very good, well thought-out replies on this thread, and many of them resonate with me. I can safely say that it isn't just one thing, and it can vary depending on the patient and the situation.
BamaBelle mentioned the desire to feel cared for and nurtured. As a playdoc, I do enjoy taking on a caring/nurturing role that I don't always get to do otherwise.
JimmyJohnson also echoed many of my thoughts. Many things about an exam are intimate in nature. Yes, the patient is surrendering control, exposing his/her most private areas and allowing them to be seen, touched, and even penetrated by someone who is not their spouse or boyfriend/girlfriend. This flies in the face of well-established social norms, yet because it's a medical situation, all those rules are completely cast aside, and that which would normally be completely unacceptable is deemed not only "okay" but good and necessary. It can be mind-blowing when you really think about what is actually happening. This is particularly true for genital and rectal exams, but it's not just that. When I briefly run my fingers through my patient's hair to examine her scalp; when I lightly palpate all over her neck with my fingertips; when I slip the head of my stethoscope just under her gown very close to her breasts -- in all of this, I'm entering her personal space as very few are allowed to. And then when it's over, it's over. She gets dressed, and we just talk, interacting in a completely platonic manner (similar to what might happen after an exam at your real doctor's office).
Dr. Stiffler makes a good point, too, about the "unspoken" aspect. In most of my med-fet fantasies over the years, there is an understanding between my patient and I that each of us are enjoying the experience at least a little, and yet nothing is ever explicitly said, and nothing is actually done in an unprofessional manner. In my real-life exams, it's usually the same way. I may get mildly aroused at times, and often I can see physical signs of arousal in the patient, but nothing is ever mentioned during the exam. So there is often a sensual aspect, but it's subtle.
I will add one more thing that I personally enjoy about these exams, and that's plain old intellectual curiosity and exploration. I remember the first time during a bimanual exam when I felt a patient's ovary move against my intravaginal finger as I varied the pressure with my hand over her abdomen. I also remember the first time I successfully inserted a Foley catheter. Both times (as my patient could attest) my face just lit up as I discovered something new. And I always enjoy it when I find a patient's cervix with a speculum. That's not sexual to me -- it's just an awesome sight. Since I don't work in the medical field, these are things I probably never would have learned or experienced otherwise. (Seriously, where else as a non-medical professional would you find someone willing to let you do such an exam or procedure just for the fun of it?!)
So for me, there are just so many things to love about med-fet and exams in general. It can convey a sense of caring in a very personal way; sometimes it can be a turn-on; usually there's something interesting to learn if you pay attention; and overall it's just a lot of fun with a good patient.