I think that once Riot released Mecha Kha'zix, they should have realized the benchmark that Legendary skins need to pass in order to BE legendary. I love this Kayle skin, and yet I do feel it doesn't quite reach it. After all, Kha had a recall, VO, new animations, evolutions and even a new joke modified. Kayle replaces quite alot, yet the Ult doesn't have a futuristic taste, the particles are very thin and bright (hard to distinquish quickly in a fight), there isn't a tech halo or the like for her lightsaber E.
That said, the floating / wing twitching is absolutely stunning. She does feel a bit small though, and the face seems a bit off. Like somebody took a human face and smoothed it out like clay. Left hand or right hand, really I think that the image might have been facing the correct way at first but they mirrored it to display more of her features.