I think everyone remembers the original Dragons Lair by Don Bluth. Made possible by the advent of Laser Disc, this arcade game was a first of its kind to try to create an interactive cinema for the viewer. The interaction was simple, you had to watch the animation unfold intently, just like with a traditional film. However, at key story moments, the screen would flash indicating the direction to move / interact and you had to respond in time.
If successful, you would trigger animation showing the movie progress in a “success” state”. If you failed, then you got to see animation showing a “fail” outcome. Very binary and simple, but also very exciting at the time.
Since then, a few other games have copied this paradigm here an there. In essence this is branching story at its simplest. However, the story never really veers off course, the only option is to not fail and see the film through to its end.
The Act is a new app that follows very much in the same footsteps as Dragons Lair. Its full film quality 2D animation, but uses the touch interface to add a layer of subtly to the affair. The core mechanics are basically the same, you must solve each challenge to continue the story, or stay stopped. The main difference being that each challenge is a series of scenes where you drag your finger back and forth, adjusting to get the win outcome, rather than flinch reaction moments that play throughout each section.
Overall I found the concept is simple, dated, and mildly entertaining. I see a lot of opportunity going to realtime assets for this type of storytelling, but using traditional animation, for the time being, seems to severely limit the possibilities to the same ones we had decades ago.