It really is pay 2 stay with the meta, I've not bought either of the expansions and its either a horrible grind to get them or paying 60 bucks for 10 cards which you really need to compete against others.
The only thing you can do as a new player is play Arena, and those you can only do one of per 3 days (unless you make a profit in Arena but then you have to know alot of stuff already about hearthstone).
