keeveek: EArn achievements to earn even more achievements! Awesome!
deavir: Oddly they are not using the achievement system. Turns out there are achievement cracks so it would ruin the card system. Sounds like it's time in game along with very vague other criteria. So start the game bots or you will be a newb because your games are not the 6 that playing matter to level your account.
At the moment it's restricted to game time yeah, although they're looking into adding additional rules but they're not sure what yet. You can only earn a couple of cards atm, typically about half of the available ones, the rest you'll have to trade for. A little bit of playing will get you to your max and I don't get the impression it's going to refresh or something so no need to idle unless you really don't want to play it :)
I'd see it as a nice bonus to get if I pick up a new game and it has this, then you can work to getting some game related stuff for your chat or profile, including a badge.