InDesign's interactivity plugin is adequate if you want to make books with pages consisting of discrete units of pic, text, video etc. But it is utterly useless for my field where I need to create a free-form interactive books: highly illustrated children's fiction and non-fiction picture books, where cut-out elements move, interact with each other and transform.
There, the only game in town is still animation tied together with bespoke coding.
There are a few simpler entrants into the market; Moglue and INteractbuilder, to name two. But they are currently too simplistic and quite clumsy products to use. Even drag and drop app builders like Gamesalad are better (though they lack adequate page position tools). There is definitely room for a killer app in this field. Something that links page position with simple animation tools and interactivity.
Everyone I know is crying out for it.
Publishers are currently spending (wasting) a fortune on this 'problem'.