I don't even know if its something you can explain anymore, about what makes a good set. So long as the basics like hot, confident model with good poses & a cute outfit, great photography, good, interesting location are all there, I think the rest follows.
The sets sitting at 99% all are pretty varied to me, so who even knows?!
I love those photos of Frolic - she always looks like she's having the best time

Frolic is hot. (Those eyes! That butt!) And Carrina is hotness personified. (That was me that asked you on FB if you had more sets of her waiting in the wings.)
Fische summed up a lot of what a good set needs. It helps if the set says something about the girl (like a cosplay set if she's into that, for example) or shows off her personality. Sometimes girls, especially Hopefuls and newer SGs, fall into the "sameface" trap where their facial expressions don't vary much, and it's harder for the viewer to get a sense of her personality. But sometimes it's all subjective and it depends on whether a particular girl "clicks" with the members at the time.

Suicide Girl sets are sequential art; they tell stories. The MacGuffin of the story is always a reason to get undressed, (or on the rare occasion, to get dressed). That reason can be as simple as undressing for the sake of undressing, or disrobing as part of a wistful contemplation, or changing cloths to fight crime, or to commit crime, or, well, on and on. Usually it's a happy story, a personable story, now and then, a secret story.
In the best sets the poses continue to be informed by the memory of the clothes even after their last vestiges have disappeared.

It's 3:30 in the morning; there's a good change this is sleep deprived B.S.

Some good story? a lot of SG looks the same in all sets, must be everytime something different.

Engagement and a storyline.

Also, I want a lion rug.