OK (just nipped away to check some vital background facts)
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Acclaimed, clearly, because it features twice in the Whoverse (still not too sure I like that abbreviation, but it'll do). City of Death (Tom Baker's Doctor in 1979) and Sarah Jane's Revenge of the Mona Lisa in 2009.
Oh, the actual painting, I hear you insist: aesthetic gurus insist it's partly her assymmetry that draws us in to figure out why the view over her left and right shoulders don't quite match up, so our brains decide to concentrate on her, instead. Come-to-bed eyes (or just got purring out of someone's). Looking straight at you, when profiles and angled poses were much more common. She's looking back at YOU and she seems to like what she sees!
Just a hint of cleavage and that ready-to-slip-off-the-shoulder drapery.
And Leonado's sfummato - smokey/ fuzzy edges that means she is -literally - easy on the eye. Straight gentlemen here would have to tell me if she is particularly attractive (try asking me about Michaelangelo's David instead) though the model gets pretty much the same rendition as his Madonnas and angels, but with out the complications of religiousness or baby-Jesus-wrangling distracting from the one-to-one between viewer and sitter.
I'm more of a quattrocento girl to be honest; I'll have another little think about other runners and riders...but enough for now. probably.