As people said... It's hard to believe what it's your first game. It's well scoped, has a lot of content, has great progression and complex mechanics described very well in levels.
It might be a little bit hard for some people to force themselves to get all stars to unlock the next zone so I would suggest to lock only super hard puzzles or "bonus pack" and allow players to complete puzzles on their own pace.
Thanks a lot for the compliment, I can't put into words how much I am happy to hear this.
We actually did a lot of small projects separately before, but this is first time we actually worked all together and our "first" serious project that I would actually call a Game.
There should be a progression system that allows to play multiple levels, not just the next, so if you get stuck you can try another one, while there are also "Bonus" levels that unlock only under certain conditions (no spoiler).
But you are still right, some levels are currently kinda broken, you can think of them as a placeholder, just the idea is right, we are still working on the level design and could make some major changes.
Consider joining us on Discord to give us more feedback and follow us on our journey! Thanks again!