I like it.
I especially like it that you don't see immediately if there's a ground or not. I mean, it is
recognizable - you just have to look carefully. But it's a good idea for increasing the difficulty.
Also I don't mind the gravity or speed - I think it's completely okay that every platformer has it's own player speed and gravity. For example see Sonic games or Mario games. Learning the world physics is part of the game IMHO.
The monster graphics should better match the style of the level blocks and the main character.
You could add some more particle effects for collecting stars or jumping for example. More colors, more bling
Regarding the camera: our Marte engine camera has a maximum speed factor as a parameter. If you set that to some value > 0 you should get a smoother following camera for free
Otherwise create a separate follower object that uses tweens to follow the player and the camera follows the new follower object.
Bugs: Yesterday on level 2 it happened that I collected two stars quickly and the counter only showed 1 star collected
I also had the double sound effect when jumping.
Keep on going, Gornova - it's a fun game!