At first it was painful, I kept dying very fast but one you get the hang of it it becomes pretty fun ! The visuals are honestly really good looking and cute !
Though, I still do have some comments :
Before reading the info, I thought the balloons were stationary, but they're, if I understand correctly going up ? I may be wrong, but if that's the case, more visual cues would have been welcomed, like some wind effects or a moving background (I do understand that it can be hard to get that movement feel while keeping that pixel art aspect, though !).
Also, it took me a little bit of time to realize that I could double jump, a tutorial or a text on the screen to indicate the controls would have been welcomed.
Gameplay wise, the movement speed is very fast. Some people will like it, other won't, personally I like this fast-paced gameplay and I think it fits well with the arcade-platformer genre !
Finally, that was very frustrating for me to die to rocks while landing on top of them (I feel like they should only kill you while under them).