The name for this one is:
Consistency, Redundancy and other closing thoughts.
The biggest issue that I see with Priest is overall lack of consistency. Now take note that lack of consistency doesn't mean overpowered or underpowered necessarily. What it means is that the performance of priests swing a lot from game to game, depending on a number of factors.
Sometimes the stars will align. The priest start off with Northshire cleric. Follow up with a divine spirit or a shadow word to shut down the early play of the opponent. He enters the mid-game with total control and card advantage, and never lets go of this. When the opponent in his desperation plays his legendary to turn things over, it is then swiftly snatched by mind control in order to seal the game.
That is the ideal case for the priest. And in this case, the priest might actually be unbeatable. But it might as well look like this.
Turn 1, the priest mind visions Deadly poison. Turn 2 the priest draws into Northshire cleric, but it is immediately killed by the buffed dagger, not even giving a single draw. From here the rogue opponent follows up with nothing but strong 4 attack minions like nether drake, azure drake and goblin auctioneer, leaving the priest's shadow words powerless. When the priest finally gets to play mind control, it is already far too late as the field and card advantage of the opponent is too big for even mind control to turn the tide.
Most of the time, the play of the priest will lie somewhere in between. But the problem arrives exactly at the bordering cases. Because the priest either looks extremely overpowered or completely powerless.
You might ask, isn't this the same case with every class? Doesn't a good or bad hand decide the strength of your play for every class? And the simple answer is: not in the same way. One of the things that hurts priests in this case is their lack of redundancy. Now lack of redundancy would normally be considered positive but in this case it basically means lack of cards that does the same or can do the same.
2 quick examples
-Mages for example can inflict 2 damage to all minions with Blizzard. But cone of cold can do pretty much the same thing if you summon a spellpower minion like Bloodmage Thalnos, with same mana cost too.
-Paladins might be facing a chillwind yeti. He can run one of his recruits into the yeti and then finish off with the truesilver champion. Or he can buff said recruit with Blessing of Kings and have it deal with the yeti alone.
Both cases are examples of cards with comparable costs that works towards the same goal, and I am sure most of you could come with more examples like this. Their effects differs and in each case, you probably know which cards you would want the most. But it is not really a matter of choice, as most of the time the game decides it for you and you might actually run all of the cards mentioned for maximum chance of being able to deal with said situation.
Priests differs through in this case. There is barely any overlap and their cards works in all sorts of ways with very few of them interacting. There are for example no case where a minion can be dealt with by both type of shadow word. This is what leaves a lot of the priest cards so situational. They work best at a given time against a given kind of opposition and there is not a lot of flexibility.
Is this balanced? Can it be balanced? Well in theory under the normal definition you could get a balanced winrate for priests assuming that they were dominating just as much with a good hand as they were getting dominated with a bad hand. Assuming both cases happens about equally as much.
But I think most of you would agree that it is not very good game design through, when the priest can tell from the very starting hand, whether they are sure to win or sure to lose. It doesn't help either that their hero power is completely useless in the opening game either, where as other classes might be able to supplement a bad hand by using their hero power until their cards becomes useable.
This will probably be the last part of my blog series. I hope those of you who have read to this point have enjoyed it. I didn't get to talk about the stronger cards of priests that much, but since MC is already getting nerfed, then there isn't really much relevance with the current trend in the highest leagues in constructed. Ask anyone and they will tell you that priests are getting owned.
Just for funsies I also made a small album containing some cards I would like to see changed/added for priests. Feel free to take a look: http://imgur.com/a/Vta1v
Have fun hearthstoning.