Wow, thank you so much for your thorough feedback!
As for the resetting, I sadly don't know why it happens. The game normally saves every time you go into the menu and should not reset as we tested it ourselves it did not do that but had others try and it did, I honestly wonder why.
For the world we did originally plan to have a different cave atleast but considering the time limit did not get it done, I barely managed doing all dragons. I don't know if we'll expand on it, we already also thought about it but not sure yet, we'll see what the future brings!
Very valid. As I played through myself I kept thinking it'd be nice to get something when you get all milestones but then again due to the time constraints we couldn't do more sadly. As for the end you don't really get anything for having all milestones, sorry to disappoint! You could only then prestige and get quicker through all worlds, that's what we managed to do in the time frame.
Your feedback is very appreciated, in case we will work further on the game we'll definitely take your feedback into account!