You have a pretty cool concept here. I sadly didn't get to beating the game (I opted to stop at the level shown below), but here are my thoughts based on what I did play.
As others have mentioned the level design in this game is quite good. Levels ramp up in complexity quite nicely, and the new mechanics like the fireworks, toggleable platforms cracked platforms, and gravity switches work well with each other. I did seem to be able to skip a few segments with the fireworks and some good timing, but I don't think that's the end of the world; it's fun to have the occasional skip like that for the player to find and feel clever about.
Despite the good level design and neat mechanics though, I really struggled to click with this game, mainly on account of the controls and the bugs. The controls were a massive pain for me to come to grips with. Grabbing doesn't need to be a separate button from jump, and down isn't an intuitive choice if you are going to make a it a separate button. And if it is going to be down, why doesn't S also bind to it (given that W A and D work for jump, left, and right)? I also didn't find space or mouse-click to be the best for fireworks given that I had to use the arrow keys; Z, X, or C would have been a good extra button for that.
The fireworks also feel quite rough around the edges despite how interesting of a mechanic they are. They send the player flying way too fast, and there's very little leniency on the timing (some sort of buffer would've been super appreciated). Moreover, the angle they send you had doesn't seem to be the same every time, and I still haven't figured out the logic behind when it sends me upward, when it sends me downward, etc. Should you build on this game in the future, I suggest slowing down fireworks and have them shoot you in the same direction every time; straight forward, no shenanigans.
Also, there are a few bugs that I ran into a lot:
- Sometimes you can grab on the very outside of a platform, after which you won't be able to jump.
- Sometimes I'd just get launched into space when trying to jump. Not sure what's causing that.
- This isn't really a bug, but the cracked platforms will disappear if you so much as graze the edge of them. I think it would be more intuitive for them to disappear after you grab and then jump off of them.
There's definitely a good game to be made here, and the levels and mechanics are conceptually very well designed. With a lot more polish and some fixes to the rough parts, this could be pretty solid.