It's extremely interesting to see the way their incentives are structured. Both games use in-game gold to let players buy goods. In Hearthstone you can buy card packs or arena entries and in Heroes you can buy new heroes to play with. Both games let you earn gold by playing in various ways.
The big difference is that Hearthstone rewards you for winning, while Heroes rewards you for playing. I've found myself get more drawn into Heroes because of this.
In Hearthstone three wins will get you some in-game gold. In Heroes you get experience for playing any game whether you win or lose. That experience causes you to level up and at each level up you get gold.
Both games have daily quests. Hearthstone daily quests usually take the form of "Win three games as a certain class" where Heroes daily quests are usually "Play two games as a certain hero type."
Can you see why Heroes gets more of my attention? Any time I play a game I make progress toward a level up or completing a quest. Even if I go on a losing streak I still have made measurable progress. In Hearthstone if I go on a losing streak I get nothing. If I stop playing for the night after a losing streak in Hearthstone I feel deflated but when the same thing happens in Heroes I feel just fine.
Both games are really good, but it's amazing how much the incentive structure can affect the fun I have in game.