It's best summarized as such:
In proportion to the rest of her body, her butt is a bit too big. Her waist is thin, her legs look like they're ready to break at the ankle, but her thighs look like they've been stuffed beyond belief, and overall, her ass is just too much.
Additionally, a few people I know, including myself, are questioning the design path in removing the mouth-cover of the helmet in both kinetic and Ethereal, considering the silhouettes seemed like they were a full mask? I understand for the ease of designing the facial effects, but overall, it does not make much sense for the mouthpiece to explode into existence on concussive alone. The mouth seems incredibly out of place. Mind you, a trade in covering the mouth on all ends and having it uncover her mouth for her more active emotes so that the design isn't completely removed, but all in all, the "remixed voices" seem more droid than human, making the sudden introduction of human lips really awkward to me.
EDIT: Allow me to go further into the mask argument. Full face masks have a job they do, and they do it quite well. You look at them, they portray something artificial, something new, something different than what is really underneath. The teardrop mask of Sona's helps portray her sleek design, pushing its bill further, while providing something interesting to look at. Suddenly, there is a massive hole in that, the mask looks more like a tick or a leech strapped over her head, like some masquerade mask.
Take a look at any other face masks that are used by popular musicians, namely the three that come to mind: Joel Zimmerman (Deadmau5), Thomas, Guy-Manuel. Removing the lower sections of the mask would remove half of the identity and reason. Joel has his Mau5head because it's just something new to look at, something interesting, something silly. Daft Punk's masks was for the mystique, as well as pushing the group's theme: Robotics, Androids, things of that nature.
When you remove a full face mask and replace it with a half face mask, it goes from looking like something silly, interesting, mysterious, to looking like an extremely tacky super-hero, which is what Kinetic and Ethereal come off as to me. The artificial sensation falls away. You no longer have a thing of music, you no longer have a person there, just someone trying to cover up their identity while pushing music to the masses. As a whole, remove the mask itself, or make it full. A robot brought to life by music (daft punk) or just someone who enjoys sharing their music with everyone, with no worries about holding a theme(Deadmau5).
[Listen, you can't deny that these proportions are fucked](http://i.imgur.com/GL8EeAe.gifv)
**Her thighs and knees suffer from clipping, her lower legs get to, at the most, a third in size to her thighs.**
Her knees alone are far too thin. Riot, seriously, it looks like someone stuffed one end of a pillow, sewed it shut halfway, and just left the other half un-stuffed. It's ridiculous. I'm not complaining about sexualization, I'm complaining about either blatant proportion problems with a skin of this quality, or blatant over-sizing of a part to pander to the side of the player base that has a hand off the keyboard half the time.