I think you're good to release it with 30 minutes of levels then add more later with updates. Then if it gets popular them do some themed level packs as IAP.
this is exactly what i am planning. i will release 12 levels on the first version and then add 3 stage with each 12 levels so the game will have 36 levels what is a lot for such a game. the thing is that it is not hard to add now 36 levels on the first version but i try to make each level very unique and add new behaviors and enemies each level so the player will not get bored.
i have a level (8) where my character can fly after drinking a potion drink. and one level the left/right button disappear and there is a auto force so the player always run and you need to avoid traps and shoot enemies. i am now working on a level where there are no lights and the player need to find the treasure in the darkness.
so it is a lot fun and i really like playing the game. i also improve every day the game performance.
i am really proud of what i have done until now with this game. its the first game i can say that has really potential to become a winner. (i hope
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