I just wanted to type out my thoughts on the current Shadow Priest.
First off; I dislike the Shadow Orb system, since this used to be exclusive to Warlocks in the sense of Soul Shards, then eventually, Paladins got Holy Power en we got Shadow Orbs... it doesn't feel special, at all.
If we do have to have those orbs, it felt better in Cataclysm, where Mind Blast was your spender, instead of a generator.
It felt much better having 3 DoT's with 3 massive, loud, harsh burst.
Great even, it felt so good just having that one-time massive damage which you could time to just mess up someone so bad if done correctly.
Now it feels so... petty.
Having only 2 DoT's, don't get me wrong, their damage is great, feels dull.
You cast Mind Blast with medium to high damage, with a pretty big cooldown to generate an orb.
With the only way of generating more orbs is proccing more Mind Blasts or casting a Shadow Word Death, and using it all to cast a medium to high damaging burst with a low-duration pretty strong DoT, feels boring in my opinion.
Don't get me wrong, Shadow Priests are strong and I still like playing it, I just liked it more before Pandaria.
My suggestion would be, give us Devouring Plague, Shadow Word: Pain and Vampiric Touch as main DoT's [albeit weaker versions since you now have consistent 3 DoT's.], no changes to Mind Blast, Use Psychic Horror or a new Shadow Word or Shadow Word: Death as Orb Spender, and make Shadow Word: Death much more mana intensive but spammable like Execute, or make it so that Shadow Word: Death uses up 1 orb, always, unless in execute, where it can be cast once before going on CD.
These are my 2 cents.
Also, since you will be weakening our DoT's significantly for this to work, maybe introduce a new spell; Shadow Word: Infect or Plague or whatever, something that spreads Shadow Word: Pain through all targets, albeit at 50% effectiveness and proc coefficient.
Having Pain spread at 50% effectiveness and proc coefficient, it occured to me this is extremely strong, having no proc coefficient on Mind Blast maybe more fair.
I also posted this on the Blizzard forums.