I personally am really excited for Diana. She's got so much that's got me excited.
The fact that she's an AP jungle, gives her immense potential, because League doesn't have much of that (AP Amumu nerfed, Fiddlesticks only functional extremely situationally and arguably better laning as a counterpick)...
Also she's the first champion whose lore really got me interested in quite a while, the "Embrace the Heresy" vs "Protect the Faith" discussions are really a lot of fun. On top of this, the back story is especially engaging because I think there's a little more hype/quality in the relationship between Leona (who is, btw, an amazing champion) and Diana.
Overall, I'm stoked for Diana, anyone else? Or anyone have any specific reasons?