I'm personally terrified he might lose his identity. I know I won't be able to like every aspect of his changes simply because I like him as he is, but at the same time dislike how simple he is (and that they nerfed his brief top-lane superiority ^^). I also have the basic fear that he might become too OP and using him will be the same as using Lee Sin (i.e. you use him because he's good, not because you like his style/theme).
Also, I have been burned before (Poor poor Karma, where are your FANS gurl? Where is your Ally/Enemy tether gurl? Where is your mid-year mage rework gurrrl? :P)
But I am super excited for the change anyway, because it also means he might gain new roles (return of top/jungle options?) and some of his abilities might become something your team actually NOTICES the effect of (Did Taric ult? What's Taric's Ult? It's that disco ball thing. Ohhhhhh *dance*)
So, what are you hoping they keep? What are you hoping is changed? What fills you with a terror so deep you cannot sleep at night (possibly not Taric related? Need to talk? A shoulder? Someone to Imbue you?)