Just an FYI for those currently playing or considering purchasing this, it appears that Chapter 5 is unplayable in the current version.
Without spoiling it, there is to be a reveal in the beginning of the chapter, very near the beginning, after the intro, which only results in a black screen. I see from a few reviews others have encountered this as well so I don't think it's device/iOS specific.
So you can fully complete the first 4 chapters, obtain all tags, get all alternate endings and complete the first 4 Extra chapters. But then you're stuck (the last 6 Extra chapters unlock through various chapter 5 playthroughs).
Otherwise I had not encountered any problems playing it. Never played it before but really enjoyed it and like these types of games. Controls could be improved upon and of course native iPad (retina) support would be a bonus.