The game's style and atmosphere are quite nice, but it is definitely too strict on the player.
Everything seems to be done to sanction the slightest slip-up, from the tiny spikes forcing a perfect trajectory after a couple of big ones, to the black wave progressing faster than the character and punishing you for mistakes you made earlier. As others mentioned, the double jumps are not quite working like one would expect either (and only on a descending trajectory, I think ?).
As someone who is still learning how not to frustrate players, I now try to have my games tested as early as possible during development phase, and to make anything new players stumble upon at least slightly easier.
This could still be a very enjoyable game if it was a little more lenient.