It's not like she was famous or even very beautiful. Don't get me wrong I think it was a masterpiece, but I have seen better from Da Vinci (hence The Last Supper). I know she was the wife of a friend, and might have been in an affair with Da Vinci (correct me if I'm wrong), but I don't see why it was so popular.
I think it's so famous because Leonardo Da Vinci painted it and there is so much speculation surrounding it like, is this Leonardo as a female? Who was Mona Lisa? Why was she painted? as many people have questioned who she is, Did he paint her with eyebrows? I think it's so famous because there's so many unanswered questions about it also the 'mysteriousness' of the woman, people think she looks sad, happy etc. How much detail Da Vinci put into the background and the fact many people have modified it like Salvador Dalí painted the 'Self portrait as Mona Lisa' Andy Warhol did 'Thirty are better than one'
cuz her eyes follow you everywhere you go and the guy is famous for it... it was the only thing like it during its time
Gosh, well this helps a lot. Thanks Leeks :p. But yes, so much mysteriousness.