Honestly, I think she just sucks. Every other support in the game does their job better than she does. Janna, Shen, and Morgana all provide shields and have more CC than Orianna does. She just has that stupid ball which everyone can dodge. Lane harass? Just move past the ball and its gone. Even with a melee champ.
If you can't hit your harass with the ball, then you aren't good at the game. Or's harass range is amazing and if done right your lane opponents will have to constantly worry about where the ball will be next.
Her shield+ speed boost make her difficult to gank, and she's great at saving your team mate's asses. Oh, and her ball can also act like a free sight ward.
She's similar to Lux in that she's a support that plays like an AP carry. If I weren't saving up for Ezreal, I'd buy her right away after facerolling with her last free week.
And then I become greeeeeen like the hulk and I feast off the flesh of the haters.
I think Orianna is fine, she just requires a lot of team coordination and has a very high skill cap. If she does need a buff, it would be to increase her AP ratios slightly because as of right now, they are somewhat low. Also, Orianna has quite a bit of CC (a slow and a flip) while still providing nice utility in terms of a speed boost and shield.
I main Orianna and I can assure you that if they buff something about her (her AP ratios, number or give her some more utility) she will be too OP. Unless is very small of a buff, in which case it won't matter anyway.
I'm used to playing AP carry with her, great damage early/mid game, awesome support late game, good at teamfights and can still pack a punch at late game to squishies (hell, even to tanks if you are fed enough).
Also, not many champions can out harass Orianna in lane if she is good. You won't escape from hers+jungler ganks.
Hope the community continues like this, ignoring her potential so I can have her for myself :$.