Hearthpwn

As with any Control Priest deck, you're hoping to make favorable trades.  The main difference with this deck is it eschews some of the more potent early game for Priest (Auchenai Soulpriest & Circle of Healing combo) in favor of the classic Wild Pyromancer and Power Word: Shield duo.  What results is a deck that is less punchy vs. decks that flood the board early (Mech Mage, Facehunter, Zoolock) but can still hold it owns after stabilizing between turns 3 and 5 with cards that give you favorable trades (Dark Cultist, Blackwing Technician) to swing things back in your favor and protect your life total (Sludge Belcher) to pave the way for your strong late game (Nefarian, Ysera, Dr. Boom).

Wild Pyromancer/Power Word: Shield/Velen's Chosen:   These cards are primarily in here to synergize with your lead-in toDragonkin Sorceror but to also stem some of the early game pressure that faster decks will apply.   If you find yourself in need of making favorable trades, Twilight Whelp has as many as 8 triggers to get its Hold buff and a Power Word: Shield can give you the early game presence you need to deplete your opponent of their early threats.

Dragonkin Sorcerer:  As Kripp said in stream once, if there's any class that can use this, it's Priest.  This guy can be a midgame monster to deal with for the opponent.  With Priest having cheap and efficient buff cards, you can get a lot of value from this guy.

Lightbomb: This one is a must sometimes.  You won't always use it to get a big clear, but it's won me several games and has synergy with one of your Dragon triggers, Volcanic Drake. 

Vol'jin: I've always felt like this was a strong card, especially if it's out of the current meta.  People rarely expect you to be running Smite, so it's easy to get value with this.

Nefarian: No Dragon deck is complete without a big, scary beast at the head of assault.  The father of the chromatic dragons is no slouch and can be an ace in the hole of sorts sometimes, depending on how kind RNGesus is to you.

Ysera:  Anti-control tech choice.  I find this card invaluable vs. Control Warrior and probably outperforms a lot of the other choices that could be inserted in her place at this spot in the curve.

Emperor Thaurissan: The king of midrange.  No card does what this one does, making it invaluable.  It came down to this and Sylvanas Windrunner for me.  I'm just not a big fan of Sylvanas in the current meta.