It was an incredibly difficult list to make. Descent of Dragons is one of the most incredibly powerful Hearthstone expansions ever printed, and takes me back to The Kobolds and The Catacombs era; in the right direction.
Some criteria very quickly. I do not list any Commons on this list; Community Cards are very cheap to craft, and you'll be drowning doubles of them by the end of the first month of the set, even as a free player. I'm also saying that disqualified maps will require a lot of support from other expensive maps to be good, which leaves out maps like Ancharrr which I think will be the cornerstone of a new Pirate Warrior. These cards don't necessarily define the deck (although some do), but all of them are great full-fledged cards that can fit into at least one type of deck that I think is common.
Druid: Breath of Dreams
2 mana, draw a card and gain an empty mana crystal. This text is powerful for anyone who has been playing Hearthstone for a while. This is the original recipe for Wild Growth (which was supposed to be nerfed at 3 mana) that also draws you a card, with the minor inconvenience of having to execute a few dragons (some of the strongest cards in this set.
Hunter: Stormhammer
Hunter typically runs Eaglehorn Bow and the Secret package in several types of decks, whether Midrange or Aggro, or beast-themed or whatever. Stormhammer is very much like Eaglehorn Bow (both are 3/3 mana weapons that “gain charges” if you do something), but deceive dragons rather than secrets.
Hunter already has a lot of support for dragons (not many people remember Witchwood had a pre-built Dragon Hunter), so this should be a very easy map to use.
Mage: elemental allies
1 mana, draw 3 cards. All you have to do is play elementals two turns in a row. Easy to complete with a crazy reward. It reminds me a bit of Aluneth but you can control when it turns off.
Paladin: Sanctuary
I had a few options that I thought I would put here, like Sky Claw, but ended up choosing Sanctuary. A 3/6 with Taunt on turn 3 is really good, and even better on turn 2 if you do. The activation requirement is pretty easy at the start of the game, and will increase exponentially if it ends up being a slower meta, which I imagine it could be (a lot of cards here push Midrange and Control decks) .
Priest: Fate Weaver
He has a good vanilla statuette and he reduces the cost of cards in hand by 1. The only stipulation is that you have to run Galakrond, but I think it will be a solid game, if not level up. Either this will be a hardcore control deck, or someone will come up with a lucky Priest combo that uses the Galakrond package just for that. Anyway, should be good.
Thief: Necrium Apothecary
I almost put Waxadred there, until I remembered that this card can potentially both draw your Waxadred and give you a second copy, a whole mana sooner. Plus, it's just a more versatile card, and may just be a good tempo play in another deck that happens to be performing some good Deathrattles rather than a Deathrattle Control Rogue.
Chaman: Dragon’s Pack
This is essentially a 5 mana 10/12 taunt. Even better, since it's split into two bodies, making it harder to pull off. It's just good value, and a pretty clear choice for a more control-oriented Galakrond shaman. I was a hair's breadth away from putting Cumulo-Maximus here, which might end up being the best option (Overload Shaman and Quest Shaman still seem to be powerful decks), but I believe in Feral Spirit +, the original has me at through The tough times when I was just starting out.
Warlock: Veiled Worshiper
4 mana 5/4 is already a decent stat line, but drawing a huge 3 cards with it is a bit crazy. It's a huge push towards playing an augmented Zakock deck from Galakrond, which sounds like a lot of fun.
Guerrier: Scion of Ruin
Warrior, as usual, gets a lot of good cards this set, but 4 mana for 9/6 stats with Rush is really good in the more aggressive, control-oriented Warrior decks.
Neutral: Dragonmaw Poacher
This is the "meta breaker" card, and everyone should have a copy of it. If dragon decks are powerful, it's powerful, and they're guaranteed to be solid at least for this expansion. Dragonmaw Poacher exists to scare your opponent into playing dragon cards at the start of the game, and is always good at the end of the game; there are very few scenarios where an 8/8 with Rush for 4 mana is bad.