I really like the priest class. It is the class i play the most, because its fun to play.
I tried everything to make Velen work in constructed and it seems to be just not good enough.
Everything the priest has is like: this works well if...
...if velen survives for next turn
...if soulpriest AND circle of healing are in my hand when i need them
...if northshire cleric draws enough cards
...if my opponent doesn't play too many 4 damage minion
...if i have a good starting hand
so it feels really OP when you manage to get the right answer for everything, but with so many "ifs" the odds unfortunately lean towards a less than 50% win ratio in constructed above rank 10.
I think the priest is lacking in the early game, the only really good low cost priest specific minion is northshire cleric and this minion really only shines when played later in the game.
Cards like shadow madness feel really great when you are able to trade 2 for 1 and steal a deathrattle in the process, but that is yet an other "if" in the list. If you can't pull it off the card might not be that useful.
Shadow form looks great in theory. You get a mage hero power that does twice the damage for the rest of the game for only 3 mana!!!! sounds awesome. BUT the priest is already lacking in the early game, are you going to sacrifice a turn in the early game and lose tempo?
People complaining about the priest often mention the divine spirit innerfire combo. Well this only works when you have board controll so you can buff a minion and attack with it, if not its too risky to have it removed or silenced before you deal any damage. Also this combo requires a lot of deck commitment to it, you need to put in 4 cards just for the combo + any minion with high health that you might otherwise not want to play or put in your deck at all. You commit ~ 6 cards and risk not having the cards you need at the right time in the game. those cards can also affect your early game in a poor way and reduce your chance at having the board controll you need anyway to pull it off.
Mind games is bad vs rush decks or said differently, its only good vs other controll deck and priest doesnt need help vs other controll deck, only "fun" to play, but terrible in competitive constructed.
The hero power is often useless early game and priest need help early game. Late game priest would need more mana to secure a confortable position, so playing more big stuff is usually better than using the hero power. Priest could benefit with a card like innervate in that regard.
Holy nova, great card right? it is...
except for the fact that the aoe heal that is built into the spell also increases the cost to 5 mana, and the heal, well, you rarely benefit from it fully. It should cost 4 mana in my opinion. priest dont have strong single target heals like the paladin so why not a free aoe heal... same notion as circle of healing, free... (when compared to consecrate).
Mind controll, great great card. But it costs too much, might as well use deathwing if you want to remove his baord and but something of your own on the field, but wait, every class can use deathwing...
Holy fire. great card, but it competes with too many other great 6 cost cards. Namely: Sylvanas, Cairne, Temple enforcer, Argent commander, Cabal, sunwalker, black knight.
Mind blast: if only vellen could survive longer it would be great. In other cases dead card, wasted early game, priest is weak early, need to play something that affect the board.
Mass dispell and silence: those are there only to fit the priest theme, not because the priest needs it. You could argue 0 cost silence on a watcher on turn 2 is great, but the priest already suffers from relying on unrelyable combos
In conclusion, i seem to sound very negative about everything the priest is, but it it still the class i enjoy the most playing because it's FUN!
I hope blizzard buffs the priest class in a way that not only brings the win ratio up, but in a way that addresses the lack of strong early game plays and maybe reduce the randomness of relying on some card combos.