I'm sexually voracious. I really can't imagine how s/m could get boring, as it responds to such a visceral need in me. But then again, I accept that I am a clinical paraphiliac. My preferences are not even remotely "normal". And I am now desensitized to the point where a lifetime of vanilla sex would bore me to death. I think I'd rather abstain altogether.
It develops into a language all of it's own, really, once you really get to know your partner- and there is no better way to get to know them intimately. And if you use your imagination, there are just sooo many ways to play... So many variations.
It isn't just about your technical skills as a lover. It isn't even about sadism or masochism per se- although sensation is certainly an integral part of it, to be sure. It is about the delicious nature of consensual power exchange, a person's willingness to open themselves completely to you... And all that entails. Allowing yourself the freedom to feel power and vulnerability. The thrill of pushing boundaries, and allowing yours to be pushed.
I guess I have some emotional and sensory issues that cause me to desire to experience things at a higher threshold of intensity, because it takes me more stimulus than the average person to really feel things, if that makes any sense.