It’s next to impossible to predict the meta due to the three most dominating sets from the past two years rotating out. But I feel more comfortable predicting what types of decks will be tried at release.
Secret Paladin - Lots of new tools for the archetype and Never Surrender! is a very powerful Secret. Sunreaver Spy will be a staple part of the deck, more so for Paladin than other Secret classes due to the mana cost of the card and secrets. Mysterious Blade is also basically Fiery War Axe as long as you got a Secret on the board. And we all know how powerful that weapon was. Commander Rhyssa is of course going to be used and tested in the deck but whether she will be good enough with our current Secrets is unclear because about half of the current Paladin Secrets won’t trigger twice. But whether these cards are going to be enough remains to be seen. People will try at the very least. I personally have high hopes for this archetype.
Burgle Rogue - The archetype got a huge boost this expansion and will most definitely be one of the most played decks in the game at launch, most likely even the most played Rogue deck. Thanks to cards such as, Hench-Clan Burglar, which helps you against other Rogues, Underbelly Fence, and Vendetta. Tak Nozwhisker is going to be another fun, even game winning, meme card for it if nothing else.
Bomb/Mech Warrior - Not looking forward to this one AT ALL. But many seem to like the idea of this archetype; with Wrenchcalibur and Clockwork Goblin it’s going to be relatively easy to put bombs into your opponent’s deck and get value from Blastmaster Boom. And due to the Mech synergies Dr. Boom, Mad Genius, is going to be even more relevant. Mech Warrior is going to be the most played Warrior deck. Personally I hoped Rush Warrior got more support…
Imp Zoo Warlock - Zoo decks have always been strong at the start of expansions due to people not knowing what other archetypes can/will work in the meta and Zoo decks are easy to make. So, until people have discovered those, Zoo warlock is going to be very popular thanks to cards such as Rafaam’s Scheme, Mad Summoner, Impferno and their ultimate win condition; Jumbo Imp. It’s going to be relatively easy for Warlocks to play and summon imps, buff them with Impferno and Grim Rally and reduce the cost of Jumbo Imp and Demonbolt for bigger target removal.
Deathrattle Mech Hunter - While I believe that Midrange Hunter will stick around due to Springpaw still being in Standard enabling Scavenging Hyena, it is certainly going to become weaker due to Candleshot, Crackling Razormaw and Dire Mole rotating out (losing Deathstalker Rexxar is not as big of a deal in the long run). What people will try to make work is a new Deathrattle Hunter relying more on Deathrattle synergy cards, such as Oblivitron and Nine Lives and their synergies with powerful Deathrattle Mechs, most notably Spider Bomb and Mechanical Whelp. Ursatron will also be at least experimented with. I’m not expecting more Tempo/Value focused Spell Hunter using Vereesa Windrunner to see much success.
Tempo/Burn Mage - Might make a comeback thanks to cheap spells such as Magic Trick and Ray of Frost, and minions like Magic Dart Frog and most notably Mana Cyclone. These cards are the reason why Mana Wyrm was nerfed, people! Mana Reservoir also looks pretty good for this deck. And due to these spells being so cheap something like Kirin Tor Tricaster might be experimented with, but whether it’s good enough we’re just have to see. And with all these Spell Damage buff cards around even Arcane Watcher may see experimentation. Stargazer Luna is also still in Standard, so you have a card drawing engine even without Aluneth. Lots of options and possibilities!
As for the other classes I didn’t mention; I have no strong opinions or comments for those. Priest will continue being annoying and Druid less so. Shaman will play Murlocs. Duh!