100% the game in 403 death. It is a good game for what it is but It could have some fine tuning to be more accessible as a puzzle platformer for people with bad timing rather than rage game. Like :

1- Putting a gauge or a music beat which indicates when a dot is going to be spawned. People will have a better sense of timing this way or learn to have a better sense of timing . (Yeah turning the game into rhythm one)

2- Calming BGM rather than stressful one (It might be a subjective taste in music). I know that this might sound counter intuitive but music can motivate people to continue the game by decreasing stress level.

3-Removing the guess work on where the coin will spawn after picking up the key. (First death on screen might be unfair sometimes.)

There is a strange difficulty curve in the game. Collecting the coins in some of beginning level are sometimes harder than the later level because there is a lack in backtracking in some of the last levels but I think they might be a reason!

There is a potential for more platforming/routing challenge but I'm not sure if I would like them added XD.

Btw I like that the dots don't start spawning before the player moves.