I think the free coins are pretty hard to come by, at least at first. Compared to Duel of Champions, it's much more grindy - you earn coins there if you lose as well, albeit less so than if you win, but in Hearthstone you only get coins if you win, at least in constructed play (haven't played arena yet). It takes you 30 wins to buy a pack, and for a new player like me, I'm winning around 50% of my matches, so that makes roughly 60 games, at around 15-20 minutes each; that's a 15-20 hour cost for 6 cards, not generous at all.
Not feeling enthusiastic about this.
edit: I feel dumb because I just remembered the daily quests. They must give a good chunk of change.
Also not to sound entirely negative, I like the interface quite a bit more here compared to DoC - there's a suitable game log and the deck building interface is a lot better. It could use a graveyard though, if only to see what has been dropped before.