Aside from her enchanting eyes, I never got the impression that what these characters fell in love with was her looks, but rather her character and personality.
Actually she has a really strong personality that gives a bad impression at fist and actually ugly hers. Geralt though she was a snotty brat but when she was cleaned up the leader of the dryads he noticed that she can be quite cute. Yen was the same her attitude is what uglied her. Way i see it is more her mood and if she is frowning or smiling that can make her less or more attractive.
But she is not unattractive, listing the characters that found her attractive: (and i know im going to sound like a pervert ><)
there was Jarre. his attraction to her was hormonal. She must have had some physical attraction. She also didnt treat him all that well, he was teasing him and ordering him around all the time.
Gors velen: there was a guy who groped her. he knew nothing of her personality, only thing he knew was her ass was gropable.
The rats. both mistle and kayneth or whatever her was called. barely knew her, only that she kicked ass and was antisocial. Both were all over her real fast.
Cahir: feel in love in dreams they where very sensual of an adult ciri sleeping with her etc.
Guy that was contact of the rats and accompanied her: it was completely physical. Ciri only gave him the cold shoulder most of the trek
Bonhart: Yeah he did say something a kin that she is too skinny for him. But A) was mostly just messing with her
b) Skinny doesn't mean flat. He still grew really obsessed with her.
Douchess in the arena: Said she had ugly face but lusted after her body. Again Ciri was frowning and all messed up because of the abuses by bonhart.
Visigota: he got her naked to dress her wound, noted in a very defensive, scientific terms that she was indeed attractive.
Auberon: he was impotent racist elf. doesnt count
P.S. Alot of the mentions that she ugly comes out more out of Ciri insecurities more than anything else. The best that can be described is that she is a type of wild natural beauty. she feels at times that she is ugly because she has to compete with fake superficial sorceress.