Right around the time they launched this expansion they put out a new "Standard" and "Wild" format for Hearthstone. Wild is what we had before, where all cards ever released are available but standard format only allows cards from the past few expansions plus the core cards from the very base game of Hearthstone. This means the designers can finally redesign the game for balance regularly while keeping a few cards from dominating every deck.
Long term the move to a standard format is a great move for Hearthstone.
They also put pre-constructed decks in the game for each class. You have to own the cards to create the deck, but if you do it only takes one click in the deck creation screen to have one of their pre-made theme decks.
Personally, this had gotten me to play the game a ton more. I love piloting a well made deck but deckbuilding has never been a fun activity for me. Now it's like the Hearthstone designers are my personal deck builders and I love it!
Overall, I think Whispers of the Old Gods is a fantastic and much needed refresh for Hearthstone.