This game has some of the most exploitive and addictive free to play mechanics of any game I have played. The way the free crates, daily mission and challenge crates work creates this constant pressure to play every day out of fear that you'll miss out on opening as many cards as possible. When I was playing this game I would routinely notice myself playing for hours at a time without having any fun, just so I would be able to complete a challenge in time to open up another card crate.