Doing almost every daily quest for quite some time now has allowed me to build up quite a bit of gold (that's the in-game currency). I could spend a bunch of it on packs when a new set releases, but I generally prefer to do Arena runs instead. It costs 150 gold for the Arena run vs only 100 for a pack, but you're also guaranteed to get a pack at the end of your Arena run. And with the latest game update, that pack is always from the most recent expansion. So the net cost for an Arena run is only 50 gold, if you would have bought the Old Gods pack anyway.
I like the Arena format enough that it's worth the 50 gold just for the opportunity to play. Better yet, if you win enough games, the additional rewards will be enough to cover the cost. I'm not good enough (or possibly, lucky enough) to always win that much, but occasionally a good run will net quite a bit more. So on average, I generally come close.
|I've played every class but Warrior at least once in the last week, and Shaman most often.|
Said luck mostly revolves around which cards are offered during the deck-building phase. In my best two recent runs (Mage 8 wins, Shaman 9 wins), I was able to collect some of the best available cards for each deck. For the mage, some solid minions combined with removal like 2 Flamestrikes, 2 Flame Lances, Twilight Flamecaller, and Fireball - plenty to clear enemy minions out of the way for my own to attack. For the shaman, Lightning Storm, Forked Lightning, Hex, etc for removal, in combination with powerful minions like Fire Elemental, Flamewreathed Faceless, and Thing from Below. I still had to play the cards correctly during the games, of course, but a good portion of those wins were picked up in the building phase when the good cards came my way.
I still have quite a bit of gold stashed, so I'll likely keep playing multiple Arena runs for a while longer. I'm still getting mostly new cards in the Old Gods packs (well, not commons, but the higher rarities). Eventually I'll have most of the non-legendary Old Gods cards, and then it'll be time to cut back to focusing on quest completion again.