Thank you for this detailed feedback!
The levels were done to allow for a short breather in between and a bit of a “ah, yes, made it further” feeling. The pickups while not visibly collected are automatically collected for you, but yes, that could have been better implemented - I tried my best to allow for a short time between reaching the end and moving to the next stage, but that introduced weird bugs and a bad gamefeel that I had no longer enough time to fix.
Since you said you want more, I might have some good news for you. I found myself playing this myself again and again even after the deadline and really enjoy it myself, so I’m actually thinking about developing this further now and turning it into something more :)