I thought the demo was brilliant and even adding 1 or 2 hours of gameplay would be awesome to play! I think the great thing about indie games and the indie game industry you don't have to make a 40hr game experience. In fact I think making games that long would take away from the charm that is indie games. Keep up the great work!
About the game length
I decided to don't make the game too long, most because I don't wanna to give up of this project, and I not really a professional, (i don't even have a job :/ ) so I will try to make this game 1 or 2 hour long, depend on how you play, but the experience will remain with you :^D, that's everything I have to say today :^] also check the game if you didn't played yet.