Bethesda's Fallout Shelter has topped Candy Crush Saga on the US and UK iOS App Store charts.

The post-apocalyptic sim/strategy game reached the top three on both charts, for both downloads and monetary gross, less than a week after its launch at E3 2015 this week.

It has garnered praise not just for its gameplay, but for its gentle approach to free-to-play gaming, which has clearly worked.

Said Bethesda's Todd Howard, "The entire goal of this game was to do something [...] that made us smile and had more depth than other things we were seeing.”

The addictive but newly-displaced Candy Crush Saga had been in the App Store top three for three years.

Fallout Shelter is available now for iOS; Fallout 4 launches November 10 for new-gen consoles and PC.