So... concept wise this game is very very cute -- I love it! And it seems with the length of this game, a lot of effort was put into it. Great job!
The game can have some improvement on the graphics; tho I'm not sure how to specifically improve it... Maybe it's the lack of apparent-enough hue-shifting...? But one thing for sure I think it can be improved.
And then I think there can be some variations in the tiling. When I played it long enough I started to find the more-or-less identical color-scheme and tiling to be somewhat boring... Maybe you should add some decorations here and there, or maybe stone-tiling?
My biggest complain however... is probably the brutal knockback... either that or make the level design less brutal. There is one part of the stage where you need to jump from platform to platform, in a room with many moving obstacles. The first few isn't quite bad, but then there is one part where I needed to jump across two moving obstacles. How was I supposed to do that!? Every time I tried to jump across, I am not quick enough to curl my snake up before it got hit by either the top or bottom moving-red spikes (I hope you know full well which room I am referring to). I noticed a gap between the two obstacles, but I believe it is still way too difficult. That alone was bad enough, but then the knockback(s) from getting hit by one of the obstacles throws my snake off from the top platform back to the bottom... and THAT is infuriating.
Lastly I think you should make the safe point heal -- either that or make it so that when you die, you restart with full health. I hoped that when my HP was reduced to 3/16 from the fore-mentioned room -- and when I saw that I couldn't heal via safe point, I killed myself; both because I was curious what would happen and because I hoped my HP would be restored to full no matter the penalty. Well... when I died I restarted from the checkpoint with 3/16 HP. Unsurprisingly... I stopped playing at that point. Now I concur my actions weren't the noblest but still... what about the players that might accidentally hit a checkpoint under dying condition? This needs fixing. :(