So I'm just gonna try to predcit how the 23 Wild cards will impact all 9 classes. I'm mostly doing this to see what applications other people think of and if I missed certain combos. Anyways, here goes.
Druid
Quest Druid has gotten another very powerful tool with Kun the Forgotten King. At face value, he doesn't look very immpressive, seeing how it'S still just a 0-mana 7/7 at turn 10 only...but thanks to the Quest you also get 10 Armor, which can be very relevant in a lot of matchups, not to mentiont that the body will usually demand an answer fro your opponent. Even if he ends up not being included in the deck (although I don't see why he wouldn't) you're probably still going to have to account for him appearing through Discovery
Astral Communion will probably not have any impact. I don't know why they gave us this over something potentially more interesting. There's just not even enough big cards that would warrant running this. At best you could run it in a Quest deck and hope you don't brick after dumping your hand. One saving grace might be Overflow, but I doubt it will be enough.
Ragnaros the Firelord, Sylvanas Windrunner and [Hearthstone Card (N'zoth the Corruptor) Not Found] could find their way into Quest Decks, but there is little overall synergy.
Emperor Thaurissan on the other hand, might have some applications, mainly if one were to give [Hearthstone Card (Gonk the Raptor) Not Found] another shot. With Gonk dead you can discount Mad Summoner and double Witching Hour + any number of attack buffs (Claw and Pounce mostly) and actually pull off the combo in one turn without having to RNG the Dreampetal Florist that being said, this is still a 5-7 card combo that requires you to play and kill off a 7-drop (that also cannot be transformed), making it even more inconsistent than Malygos currently is. Not to mention the relatively high amount of combo pieces makes the Quest shell much weaker.
Mage
Now Mage is a pretty interesting case since it'S currently on life support. People don't seem to be that excited about Babbling Book, but I think it could be crucial in making more tempo oriented Mage builds (including Secret Mage) more viable, purely on the basis of being an actual 1-drop for a class that currently has none.
Flamewaker on the other hand feels a bit overhyped. Granted, we can go machinegun with a Sorcerer's Apprentice and a Mana Cyclone for reload, but would be more of a combo deck, not unlike the previous Cylone Mage which isn't all that great at the moment. I still believe Flamewaker is good enough to pick Mage up from the dumpster, but I don't think we're gonna get higher than tier 2.
Regular Tempo Mage also seems a bit weak at the moment...at least too weak to rely entirely on Flamewaker to carry it. Keep in mind that unless you are absolutely certain he won't get removed, you can't actually play Flamewaker on 3, and you need at least apprentice, Ray of Frost, Cyclone and Elemental Evocation to really pop off...in a deck that can't tutor any of the pieces.
Aside from the class cards Emperor Thaurissan is a strong addition to Highlander Mage (since you're usually holding a big hand and it bridges the 7-mana gap in some cases). Furthermore, N'zoth allows for another board refill by just running [Hearthstone Card (Karthut Defender) Not Found], Rotten Applebaum and Sylvanas Windrunner. Ragnaros might find a way in too, but I suspect that would be a bit greedy.
Whatever happens, Mage is certainly going to be much better than it is now, even if just by a little.
Paladin:
Now it's pretty obvious that Secret Paladin is going to return. Both Mysterious Challenger (effectively Subject 9 on steroids) and Avenge (the best secret to keep a lead on the board) should be enough to make the deck at lest playable. The draw issue is pretty much solved, although including both Challenger and Bellringer Sentry will warrant quite a large amount of Secrets. Maybe MC makes its way into Highlander Paladin as well with a Secret heavy build (read: every single available Secret) although I feel like Octosari is still a safer choice.
Much less talked about is the potential Control Paladin, that could "return". Paladin has always been the best class (next to Warlock) to use N'zoth, but it just never took off. A N'zoth that resurrects Tirion Fordring, Sylvanas and Karthut Defenders is probably the best turn 10 play for any lategame deck. What's different this time around is the existence of the Holy Wrath + [Hearthstone Card (Shirvallah the Tiger) Not Found] combo. With just 3 cards you add a 25 damage burst into a control deck, but instead of going the regular way of mowing through your deck we play it slow and grind out the opponent until we finish him off. You can go pretty light on the minion side and just use the best defensive options and a bit of draw with most of the removal spells. The challenge would be to properly balance the amount of removal and actual minions. The biggest problem with this idea would be that most other classes will just end up running N'zoth as well and it's questionable whether the addition of Tirion is enough of an upside to make a difference.
N'zoth could also work in a minion focussed Midrange/lategame deck, maybe even Highlander (just don't run Octosari or you will find a very unfortunate end).
Hunter
Hunter got some very solid additions. Lock and Load is probably not going to be competitive, but makes a very spell heavy Hunter at least worth trying. I can't see it taking up a slot in Highlander however. Value Generation isn't exactly needed for Hunter at the moment.
Call of the Wild on the other hand is way more interesting. It occupies a very interesting mana slot at 9, meaning that you can play it as a set up for Zul'jin which is especially relevant since it mitigates the downside of having to play Zul'jin for tempo/defense without having used Unleash the Beast first. With just this and a few Secrets you will have enough value to stay in the game. Not to mention the card isn't a bad topdeck later on at gives you 5-damage reach.
N'zoth and Sylvanas are also interesting. On one hand you could build a deathrattle centered Highlander build. In this slower variant Emperor Thaurissan might get good value as well. Next to that there's the possibility of reviving mech Deathrattle. Nine Lives is already incredible and Sylvanas onnly makes it better. Going light on the actual deathrattles to get the best possible outcome from N'zoth would also allow for more defensive tools. The main argument for this deck would be that N'zoth being popular makes grindy decks better and requires more value to beat them, which current Highlander Hunter probably can't.
Shaman
I see no real use for Thing from Below. There's just not enough totems at the moment to get any benefit out of it. Evolve on the other hand fits perfectly into all Shaman decks running Mogu Fleshshaper. The combo of Fleshshaper + Mutate is already busted and Evolve just doubles the consistency (next to being even more generally useful in token decks than Mutate).
Shaman can also make good use out of N'zot since Shudderwock essentially gives you a second one. Combine it with lackey generators and Hagatha the Witch you have a solid lategame plan to grind most decks into dust...the question is whether this is a better grinding gameplan than other N'zoth decks.
Rogue
Swashburglar is great for both Quest and Quest-less thief Rogue. It essentially makes curving into a Underbelly Fence much easier without the tempo loss of Pilfer (except against other Rogues). As a result it makes the Burgle package a much better inclusion in just about any possible Rogue build. [Hearthstone Card (Shaku the Collector) Not Found] on the other hand is pretty much garbage. It's a slower Blink Fox with stealth + soft taunt being the only upside. Not great when you have to consider that getting a 0-cost Vendetta on turn 3 might be more important.
Once again we have Deathrattle shenanigans. [Hearthstone Card (Anka the Buried) Not Found] allows for shenanigans with Sylvanas (and Anubisath Warbringer), while Shadowstep and [Hearthstone Card (Togwaggle's Scheme's) Not Found] enables complete N'zoth lockdown. The resulting deck might be unbearably slow and bricky, but it's gonna be loads of fun when it pays off. You thought infinite Tess Greymane was a Warrior killer? Let's see how many Sylvanas the can deal with before they give up.
Priest
I'll be honest, I have no idea how Priest is going to turn out. Vol'jin doesn't really have a purpose at the moment. Priest doesn't run 2-damage removal so there's really no point to include him anywhere. Lightbomb is a good additional boardclear which will make the slower Quest/Resurrect builds a bit better against aggro and N'zoth and Sylvanas won't hurt either in that kind of deck. Once again the question remains which class makes the best use of N'zoth.
Warlock
Gul'dan got shafted again. Renounce Darkness is for memes only, obviously, although Zephrys could probably be of use in there (if you get lucky enough to not get too many duplicates, and let's be honest that's kind of why you play the deck in the first place).
Zoo get Imp Gang Boss, which is still one of the most powerful standalone 3-drops in the game which will imrpove their winrate but won't change their palystyle. Highlander Zoo certainly appreciates it.
N'zoth Sylvanas and Ragnaros are very interesting additions to Plot Twist Warlock as both Fel Lord Betrug and Dollmaster Dorian can get incredibly value from them (they can be used to quickly charge your N'zoth with Karthut defenders or Sylvanas). Combine it with Mechanical Whelp and there's a decent strategy. Unfortunately it has to compete with all other potential N'zoth grinders, where it will most likely lose out based on the fact that it hits fatigue way earlier. Personally I'm going to revive my Anubisath-HIr'eek-Omega Agent Handbuff build, because why not, it's not like it's getting any better.
Warrior
Not terribly exciting. Bloodhoof Brave is a potentially cool card for Aggro/Tempo Warrior (specifcally Highlander), but it's probably not proactive enough. Taunt Warrior has unfortunately been nerfed through the discovery nerf, so I don't see that picking up steam all of a sudden. Varian Wrynn could potentially make it viable, but with Tomb Warden and [Hearthstone Card (Frigthened Flunky) Not Found] having pretty much essential battlecries it makes no sense to risk pulling them out on the field.
I also don't believe in Big Warrior. Warrior has no ramp or mana cheating and waiting until turn 10 to actually do stuff is just...not realistic.
Funnily enough, Control Warrior is probably also the least likely class to make good use out of N'zoth. having no class deathrattles means at best you're gonna get a Karthut wall with Sylvanas in a deck that wins the lategame through other means. It might still end up running N'zoth out of necessity just to not get outvalued by all other Deathrattle decks.
I really wish we got [Hearthstone Card (Alexstraza's Champion) Not Found] instead.
Miscellaneous
I currently see no real good use for The Curator. There aren't any good murlocs or dragons outside of tribal decks. Nightmare Amalgam technically gives you two guaranteed draws, but that's not really enough to slot into any deck. The only thing I can come up with would be a) Midrange Dragon Paladin with Murmy and a Mech Package or b) Hooktusk Rogue with the same principle (which is just an inferior version of Tempo/thief Rogue anyways, so no point).
I also can't really imagine Ragnaros in too many decks. He's a good card and there's a reason why he was Hall of Famed, but at this point in the game most decks are so heavily specialized that they have simply no space for a card that doesn't actually synergize with their gameplan. The only exception are Highlander decks of course. Hunter will probably find a place for Rag, purely on the basis of not having an 8-drop, and Mage will probably enjoy having any proactive options. He might be too greedy for Paladin though (although he could be an interesting choice in Quest Paladin....if that deck wasn't dead).
Thaurissan probably has way more combos than I listed, but I don't think most of them will amount to anything more than memes. He's probably best as just a Highlander 6-drop in Mage to smooth out the curve.
Closing thoughts
Writing this I kinda got worried that the meta might become a very one dimensionnal N'zoth slugfest for a while until the best N'zoth class emerges to kick all others off the table...who will then proceed to build the most aggressive decks possible to kill them before turn 10.
Whatever happens, i'm glad that this event exists, even if just to showcase how broken stuff can get with the right tools. If the meta goes completely haywiere at least we only have to wait until November for it to return back to normal. Pretty sure after being N'zoth-locked for 3 weeks straight will make Control Warrior look fun and interactive in comparison.