To me Hearthstone didn't feel grindy at all compared to almost any other top IAP game available in App Store. I think Hearthstone hit a pretty good balance for freemium IAP model, I never felt that I had to pay to be able to play, unlike in most of the other freemium IAP games.

I agree that classing causes a bit too predicable deck strategies, MtG felt more balanced on this aspect.

What Hearthstone got right was the flow: they had to remove instants and introduce secrets and taunts, but with that they achieved an excellent flow for a turn-based card game.