It is P2W in the way that to get Expert Cards "fast enough" you need to pay, otherwise, you are going to be "stuck" with Basic Cards for a long time unless you play the game a lot everyday.
There is a huge difference between Expert Cards and Basic Cards and if you play with a Basic Deck against someone with an Expert Deck you will notice the different after the first 3 minutes of match.
It is not a direct "P2W" since cards are random in the packs, but again, if you buy cards and dont get what you want, you can disenchant them and craft the ones you want, if you dont buy, you cant get enough cards to disenchant.
The ingame money is Gold and you need 100 Gold to purchase 1 Card Pack, Daily quests give like 10~15 Golds (not sure right now), so it takes a lot to actually be able to buy one. I think there are some special Quests that give 50 or so, but still... That is what I meant when I said "P2W". I just wanted to clarify it. xD
@Klown:
I don't think they will add Clases to the game (yet). At least, I think it is early and they are having some problem balancing Rogue Deck and don't remember what other Deck too.
Edit:
I was just derping, won 2 games as Mage, got 40 Gold. In addition, I won 3 gams and got another 10 Gold, so I had 100 Gold and purchased a Card Pack... I wasn't expecting Expert Cards, even good cards, and despite I mainly play Mage Deck, I got a Legendary Paladin Card. I was so surprised... I can say they achieved that feeling of "getting Epic Cards", because I was like "omg!omg!!111111222" when I heard the "Leeeegendaary" O_O
Side note: Don't mind the language, its spanish, just in case someone wonders about it.