This was a decent platformer with a lot of room for improvement. I think the level design and mechanics can be improved.
These are my suggestions/recommendations for this game:
- Level design - This definitely needs some work to make the game for interesting and to make the levels more unique to each other. Levels like 4 and 16 are basically the same. Level 11 was clever with the game's aesthetic, using a platform that camouflaged in order to create a death trap for the player. I would've liked to see more of that.
- Crystals - these don't really serve a purpose in this game. They are very easy to collect and give nothing in return. Collectibles should have some challenge to them, just to make them a bit more worthwhile. I also suggest that you try out using NG medals, so when all crystals are collected, the player gets a medal. Medals can also incentivize players to pursue those collectibles and allow you to create optional challenges like a "no checkpoint" achievement for not using any checkpoints throughout the game.
- Mechanics - Some changes such as allowing the player should move along moving platforms would be good, instead of having the player stay still with the platform moving beneath them. Another suggestion for the mechanics would be to avoiding adding obstacles like the windmill at level 12. Obstacles like that are tedious for the type of control that this game has, where the player can easily "stick" on slopes and circles while also having weird "floatiness" if that slope is moving. My trick for level 12 was to jump on the slope and stick to it, and having the platform flick me to the upper ledge. I personally don't think that it's a good game mechanic to have, it feels tedious and awkward to do.
- Title Screen - as the title screen moves, it cuts off some of the text. It would be better of all the text for the title screen to be visible all the time. You can achieve this with static text, with a background that moves, or limit the movement that it would not cut off the text.
I look forward to what updates you might do with this game.