I liked the visuals and the music, and the platforming was fairly solid with a nice progression of difficulty. There are two things I think are worth pointing out:
When the player is mostly going to the right or left, (for example during most of the platforming sections), it's better to lock the camera at a neutral height rather than have it move up and down with the player, which can get disorienting.
The boss's attack where spikes come up from the ground gives no sign of what's about to happen. The player has no way to know that spikes will come up when the boss lands, and that leads to taking a hit in a way that feels very cheap. It would be good to give some form of visual forewarning.
Still, all in all, great game!