I like simple platformer games like this and got through it without much problem. The levels became more difficult while keeping the simple design, and I don't think they ever became stupidly difficult, so good job on that.
The only problem I had was on level 42. I think you intended for the boxes to stack when they fall, but they don't, forcing the player to get all the diamonds and achievements they can to advance. This makes certain parts of levels just after this suddenly seem a bit too easy.
Also, all the music started playing at the same time when I got all the achievements. Not sure if that was intentional but it sounded kinda weird.