We went user controlled because we wanted people to be able to guide their own experience. We watched a bunch of people use the app and noticed people went a very different speeds.
It turned out that we show so little at a time that people went through the deck in two ways: very slowly or very quickly. We couldn't have allowed both to do that with an auto-play or video function.
When I went through it I tapped as fast as if I'm playing a video game, although not because I'm a fast reader, more because there are so few words on the screen. I don't think there's a good way to solve this, or that you need to.
It turned out that we show so little at a time that people went through the deck in two ways: very slowly or very quickly. We couldn't have allowed both to do that with an auto-play or video function.