There are indeed more levels than advertised XD At the moment our targeted regular experience is just under 4-5 hrs without 100% completion, however we're still tweaking some of the difficulties and flow of the game, so that's still subject to change, but it wouldn't stray too far from that estimated number. We are itching to get more content in of course, but we have to restrain ourselves to the budget & time available. Thanks for the question!
Viewing post in Dev Diary #12 - Smokin' Progress comments
That's great to hear. I personally think and always thought that way that a game should really have measured proportions in terms of collectibles and play time. So To me 4-5 hours is a pretty good experience. I think above 8 would feel too demanding for players.
Successful indie games like Journey and Abzu, Vane and others also manage to balance these aspects pretty well, and they usually don't take longer than 5-6 hours. So that's great to hear.