The Fallout Shelter app's breakout success took everyone, including Bethesda, by surprise. It's a casual, free-to-play game - exactly what many hardcore players hate - but it became so popular that its revenue overtook Candy Crush, the traditional King of the mobile market. Nor is it just the traditional mobile players who hopped on board: user reviews and the game's forum come from the hardcore audience. The simple gameplay inspired by Tiny Tower has very little interactivity and is heavily timer-based. It also makes the best characters available only to those who pay money for the game's "lunchbox" gachapon. So why does this game succeed where other hardcore-into-casual games like Bioware's Heroes of Dragon Age or EA's Dungeon Keeper reboot failed? It may be that the lack of energy systems and PvP, traditional drivers of F2P monetization, made the game more friendly and less demanding to play.