For me it all comes down to a woman enjoying herself and completely letting go. Ive been getting off to cuckold stuff but mostly because it normally involves the woman living every fantasy of hers. Then there's impregnation, IR, group sex...
Though most of the things that violate the community standards works too depending on the mood.
IRL I LOVE cum play and though I would never want to share my wife, I love her sloppy seconds and going down on her after.
I do have one good fantasy though of helping a virgin bride prepare for her "first time" with lots of practice, including the night before the wedding, the morning after she is dressed and set, during the reception, and on her wedding night when the hubby has too many drinks.... Of course she knows she picked her wedding date to start a family as soon as possible...