I felt that the final puzzles where too easy, with the exception of the platform puzzle. That one was ok in terms of difficulty. While I figured out that they would move together, I can see why people assume otherwise, that was unclear. What does bug me is having to restart it just because a piece went missing. A piece that was never used mind you. I can't say that I like the abrupt ending either.
But what bugs me the most is that the gum collecting was buggy. If you collect too fast, pieces aren't counted and you have to collect them again. And I think the mouths where a bit buggy this time. And I honestly don't like intentional quality degradation. The low framerate was bad.
But I liked the how note, it helps when you accidentally solve a puzzle. But then again, that only happened with the annoying fitting puzzles. I don't like the final two of those. The cog parts didn't fit together in any logical way. And the arranging puzzles plain shouldn't snap at all. But they also had issues with what piece I picked.
As for the GUI, I have only one thing to say, the bouncy scrollbars suck. It is not a good idea, and it just annoys the user.
As for the lack of quality settings, I think at least the snow falling could be disabled. If the horrible noise can be part of the quality settings, why not the snow?
And the key puzzle had me assuming that each fish had another inside it, even if it already was inside another one. And yeah, get the key, jump out of the window?