There are several dozen reasons this is a really lovely image but I would like to focus specifically on its careful use of tonality.
It is meant to be scanned left to right. The skin of the male bodied partner is exposed a hair below complete overexposure and loss of highlight detail. (Making a traditional darkroom wet print, you would probably have to split grade and burn the edge in with a 4 or 4.5 filter.)
The male bodied participant is rendered an ethereal specter; his body only begins gaining form and dimension in relation to his proximity to his partner.
The right half of the frame is heavy with a mid-to-dark range of tones. The female-bodied partner’s teeth represent the only tone in from the highlight range. This balances against the dark tones of the pubic hair in the left half of the frame–in a way the skin and high heel encircle the penetrative sex act, highlighting it.
The darkest areas of the frame are in the armpits of his t-shirt, the area shadowed by her left thigh and his right forearm and her hair.
Thus the tonal composition reduces to a figure not unlike: 0>.
What is interesting to me is the discrepancies from the figure and how they actually enhance the image. If you follow the highlight of her blown out high heels suspended in midair–a porno trope I loathe but that serves here–your eye is led in the direction of his face (where his eyes are locked on his erection as it is consumed by her body); whereas, if you are following the mid-to-dark tones, your eye descends to note the way her knees hook into his elbows.
All that definitely appeals to my aesthetic sensibilities. But it’s the way that despite the emphasis on the graphic depiction of intercourse, that I am entirely preoccupied with her calm and beautifully meditative expression.