Blizzard has slowly been unveiling each of the new class cards for their upcoming mini expansion: B̶u̶r̶n̶i̶n̶g̶ ̶C̶r̶u̶s̶a̶d̶e̶ Curse of Naxxramas. So far, they've unveiled the following:
Now they have revealed the new Shaman class card: Rebirth. At 2 mana, it destroys a minion and restores it to full life. The whole theme of Curse of Naxxramas is centered around deathrattle. Players such as TidesofTime and Trump do not feel that this card is all that useful in the current meta. The reason being is that it is a synergistic card that costs 2 mana. Take this with a grain of salt as Trump makes this assumption due to the fact that we all do not have access to all the available cards in Curse of Naxx. Obviously, this Rebirth card combos really well with Cairne, Sylvanas, and Leeroy. However, Cairne and Sylvanas are prime targets for removal once they're on the field. Thus, either you wait until turn 8 to use the Rebirth combo, or play the card on turn 6/7 and hope it does not get removed. It's these reasons that some of the top players are skeptical about Rebirth's power. However, we do know that one card that it goes great with is the Nerubian Egg. Note that Curse of Naxx will be arriving sometime this summer with only the first wing being free to enter. The other four wings' prices have yet to be determined. The meta game will fluctuate since each wing will be released on a week by week basis.
In order to obtain these class cards, players will have to complete specific class quests with pre-built decks. There's a total of 30 new cards and fifteen new bosses. Also it's important to note that players win a legendary card for completing each wing. What would be really interesting is if Blizzard finds a way to implement a cooperative type of play sometime in the future.
Source: Liquid Hearth