With this deck, you will basically be grignoting your opponent.

Game plan :

Control early game with the usual priest package of Northshire Cleric, Wild Pyromancer, Acolyte of Pain plus cheap spells.

Then, when you have stabilized the board (if you do so, because priest is horrible at controlling at the moment, which is a shame, screw you Blizzard), you will be able to grignote your opponent using Shadowform and Mind Blast, until he dies.

Don't forget to Power Word: Replicate on Archmage Vargoth if possible (Except against Warrior), pretty cool interaction, but you can also play it on Zilliax for extra healing or on a Prophet Velen if it survives, for some reason.

Conclusion :

Vry pwerful. Yes.