I just got the Hextech Annie skin last night...
And I have to say I'm rather disappointed. Given how hard it is to get, it's really underwhelming. Other than a reskin for tibbers (which looks nice I must admit), the VFX on her abilties are just meh, there's no new quotes or VO, and the only non-ability animation that's different is her recall.
I understand that it's a skin anyone can get theoretically for free (although doing so for most people will take forever).
It's kind of sad that I got more value out of the other things from the chests than I did from the rare gemstones.