Just initial thoughts and analysis also will add a star rating in the current meta/card pool
the stars are like this: (like Trumps rating)
5 - meta defining defines a tier 1 deck
4 - is in a tier 1 deck or defines a tier 2 deck
3 - is in a tier 2 deck or tech in tier 1 or defines a tier 3 deck
2- tried a bit then dropped
1- meme/awful.
Neutral:
N'Zoth, the Corruptor- 5 - the meta is not that fast that this card won't see play in a control list, goes very well with sylvanas and there's no way sylvanas doesn't see play.
[Hearthstone Card (sylvannas windrunner) Not Found] -5- this card is insane we all know that it goes very well in hunter currently Nine Lives is a 3 mana mind control with it. apart from that any other slow midrange/control deck would play her.
Ragnaros the Firelord -5- this card was HOF before elementals were a thing in standard currently there is little synergy apart from mage and shaman with only a few cards that don't see play, but in mage it's really good with [Hearthstone Card (elemental invocation) Not Found], the card can also just be slapped into a variety of decks anyway.
The Curator -3- dragons are kinda dead in standard, beasts are everywhere and there is not really a generalist murloc you would want to draw, seems situational maybe in a sort of a lackey shaman with amalgam just to draw 3..?
Emperor Thaurissan -5- key card in any combo deck and enables them, there's no way no new combo deck we didn't think about shows up.
Druid:
Astral Communion -1- was bad, and is still bad.
Kun the Forgotten King -2- maybe tried in quest druid the card is good but currently doesn't do any crazy combo without Aviana and a 0 mana 7/7 that is a dead card until turn 10 is kind of meh.
Hunter:
Lock and Load -2- spell heavy hunters value engine, but are random hunter cards for 2 mana good enough.. nah I don't think so I used this card in solo adventures from rime to time wasn't impressed by it too much (by that I mean.. best case scenario it's not that great.)
Call of the Wild -4- highlander hunter is very strong and you slot it in for a more impactful zuljin it's a really good card and game closer, think it might be run in the deck cause of mainly zuljin and it's a good card just that when it got nerfed the meta was really fast and then death knights came around, so this card got quite left behind also go outclassed by To My Side! in spell hunter.
Mage:
Babbling Book- 3 - was a decent card but nothing really there are some really bad mage cards it's a 1/1+ that bad classic card, was briefly played in the past.
Flamewaker -5- now THIS is something mage needed, now more than ever with so many cheap spells/spell generation this card is as insane as ever tempo mage is back!
Paladin:
Mysterious Challenger -3- who am I? none of your business. this + the best paladin secret in the game makes secret paladin which got a ton of support in ROS a real contender this is kind of the late game the secret paladin needs.. it currently runs out of gas and that's it.. but MC makes the deck shine again that being said I think secret paladin is either a tier 3 or 2 deck cause of the power creep in the game
Avenge -4- this is the best paladin secret in the game it's worth including even in murloc decks I think so even if "Secret paladin" is not a thing this card might see play in the more aggressive paladin decks. Edit: facepalm on the murloc paladin -> Prismatic Lens as @PopeNeia pointed out.
Shaman:
Evolve -5- slotted into quest shaman instead of mutate or in addition to mutate also good in aggro shaman.
Thing from Below-4- not as good as when it was in standard cause of no totem golem, 2 mana flametongue totem, and no taskarr totemic, but it's still a really good card and great evolve target.
Rogue:
Shaku, the Collector-?-
[Hearthstone Card (swashburglar-) Not Found]?- dunno how to evaluate thief rogue + 3 more thief cards don't think it will make the class suddenly great I am not sure how rogue does atm, but I didn't see them a lot lately. it does make the turn 2 underbelly more consistent.
Priest:
Lightbomb-5- res priest might make a return and this card just makes the deck much much better it's aoe they need to work currently they need either a 2 of in mass hysteria or to wait until turn 9.. this card just makes priest good again think res prist will be tier 1 with sylvanas being back.
Vol'jin-2- the card is decent, but I think it doesn't fit well into the current decks.
Warlock:
Imp Gang Boss -4- zoo is tier 2 and one really good 3 drop won't change it.
Renounce Darkness-1- meme
Warrior:
Varian Wrynn-2- there are some big warrior cards in boomsday, I think such deck is too greedy though.
Bloodhoof Brave -2- card is good, but it's not constructed good.
Edit: forgot hunter lol