Playable on iPhone 4S and up
Supergiant Games did a great job of getting Bastion on iPad in a way that fit well with the platform. This version has received a free update which includes iCloud support and makes the game compatible with iPhone 4S, 5, and the 5th-gen iPod touch.
Originally, the studio stuck with only iPad support due to concerns about screen size and how that would impact playability. They found the iPhone 5 to be worth investigating, which is how this all came about. From there, Supergiant concluded that Bastion would also work well enough on 4S and touch. Personally, I'd want to check out how it handles on an iPad mini.
Bastion for iPad Now a Universal App, Optimized for iPhone 5! [Supergiant Games]