I think the skin itself is great. Lots of work was definitely put into it and I respect that. If I was a Lux main I would be creaming myself. But I don't even play Lux, so you can understand some of the frustration that comes when certain champions get lots of skins and attention while others are left behind with skins from 2013.
So the issue that I have with the skin is that it's basically 10 different 1350 or 1820 skins for Lux all rolled into one (or maybe 10 'chromas' for a legendary rolled into one, whatever) which is basically an entire skin line only for Lux. I feel like they would have made a lot more people a lot happier if, instead of making Elementalist Lux, they made an Elementalist skin line for 10 champions.
And while the concept of a shapeshifting Elementalist is cool and unique, it's not a concept that could solely apply to Lux. Any mage like Xerath or magical warrior like Shen could have some sort of elemental theme applied to them that would fit.
I don't have issues with the skin itself, just the fact that so much effort went into this when it really could have gone elsewhere. Imagine an ultimate tier Shen, Cassiopeia, Aatrox, Mundo, Xerath, Skarner, Viktor, or Twitch. Can't imagine them because you don't play these champions? Yeah, that's how I feel right now. Some of these champions don't even have skins with particle effects, and Lux is getting 10 skins for the price of roughly 3. This is why some people feel shafted, because lately it seems like all the champions that already have a huge amount of skins keep getting more, all while champions with really old skins get nothing.
I want to have faith in Riot, but when they keep releasing skins for their top selling champions instead of the ones that are in desperate need, it chips away at my respect for them little by little.