If you're not going to add difficulty selections. At some point where you think the game is at normal difficulty for you, you have to make the game easier for you, because the most skilled player of this game is the developer. When the game is being too challenging it makes me feel frustrating and I was having fun but then I wasn't because it was too challenging.
The way the view keeps looking back is nice looking but that feature made the game more difficult because the player can't see much ahead making me fail and retry multiple times.
The collusion size of spikes is too big.
Sometimes I find the non-solid wall a solid wall because its color is very similar to the solid wall.
But the graphics and sounds are okay in this game. Good job.