At GDC this year, Halfbrick put together a presentation on 'The Making of Jetpack Joyride', a game which I spent untold hours on public transport playing -- and I'm sure I wasn't the only one. That presentation is now available to watch for free on the GDC vault website. If you have the time it's a pretty incredible watch.
I found it particularly interesting that Jetpack Joyride was, initially, a game that was supposed to be made in four weeks. The idea was to take a core concept in Halfbrick's earlier game, Monster Dash, and strip it back to create a one button endless runner.
If you have any interest in games development at all this is a must watch.
Head here to check it out.