@RiotVolty: How to fix Diana

Ok, so here's my take on how Diana can be fixed.
First off, something to note: I firmly believe that in her current itteration, Diana will never make a good assassin. She is completely eclipsed (pun intended) by Akali and her you'll always think "man, this would be so much better if I picked Akali" when playing her full AP.
Not saying that she's not a good assassin, or that her full-AP playstyle is bad, but it's outclassed by Akali.
That said, what she has that Akali does not is very strong AoE CC that can be used for initiation and a shield, as well as good sustained damage via passive. Now, you'll notice these are not assassin qualities. Hell, she's one of the rare "assassins" that has no real safety mechanism to get out with after she dives someone. These are all bruiser qualities.

In fact, as a bruiser, she's unique enough to have her own niche and not be completely overshadowed by another champion.

Now, onto the meat of this thread.

• Her QRR combo
Let's face it. It's an issue. It's been already admitted to be an issue. And that's fine. We can fix it.
"How?" you ask? Well, I say, tone down the power of the combo so she isn't instantly deleting people with them having no chance to retaliate. That will enable you to shift power around a bit and distribute it to the rest of her kit.
Specifically: Make QR not reset R cooldown, but instead put it on a 2-3 second cooldown. That gives time for the enemy to react and Diana won't be instantly deleting you when ahead, anymore.
Alternatively, make it reset completely, but go on a "per-target" cooldown for 2-3 seconds (similar to Yasuo) so she can QR->R out to safety.

• Her shield
It needs some love, let's just admit it.
Even with 500 AP, it's only a 250 shield with a chance to be increased by another 250.
Increase its base values for the shield. That should give her a bit of an oompf.

• Her shields orbs
This is more of a minor complaint, but when the W orbs explode, make the explosion be centered on Diana herself, not the orb. There are cases when jungling, especially at wraiths, where i've been slowed down because the explosions fail to reach one of the mini creeps because they are centered on the orbs.
If i just walk in the middle of the wraith camp, press W so that all 3 orbs explode instantly, all 3 explosions should hit all 4 wraiths. That is not the case currently. It feels a bit wonky, just saying.

• Moonfall
Her E is really nice. There's no denying that it's a really iconic ability.
However, when you nerfed it, you not only reduced the duration of the pull, but also the distance.
This was too much, and it really shows.
My suggestion is, bring the pull distance back to what it was, or closer to it, but leave the pull duration the same.
It's use case should be when the target escaped your AA range and is about to escape, but you pull them back towards you. Currently, with the low distance of the pull, you have to use it really early for it to have any effect, or else they'll just walk away before you reach them.
Basically, make her E put them in her AA range, at least.

• Passive
The nerf of it's range really hurt her jungling AND her lane pushing power. It's such a small AoE now.
It's not even worth thinking of it as AoE, it's better to just think of it as a Jax R-like onhit, since the change of you hitting more than one person is so slim.
For crying out loud, increase the AoE. Revert the last AP scaling buff if you have to, but come on...

• Misc. doodads
Decrease her R mana cost. Either keep it at a steady 50 or decrease it completely but equally across levels (30/45/60 or something like that).
Increase her Q damage. It's a bit low for a skill which is relatively hard to hit on moving targets (especially if they're going left), don't you think?

DISCLAIMER: Again, this is just a grab-bag of ideas. I'm not suggesting all of them need to be implemented as is, but some of them may fix some of her issues.