When you say transversal movement is bad you mean going up or down?
It's not fun because it's empty. It's not fun because there is no choice to do, nothing to collect or dodge(monsters mostly mind their business and deal almost no dmg) or button to press when you go from A to B. Your game right now is the equivalent of an empty mario level.
Some people said the movement is slow but it is the same speed as the horizontal movement, I think the parallax background may give the feeling that the player is moving too slow.
It's also the big amount of nothing of your level design. If you wanna make a first level a tutorial area is fine, but there is no reason to make it this big beyond wasting player time
Did the dash break collisions or do you mean its too fast when compared to regular movement?
it's too fast and works for too much. Go see any dash from any game. Even racers have more restraint.
I think you mean to disable the alarm entirely.
yep
My suggestion is to see a longplay (but better if you pick up an emulator and you play them) of Ecco the dolphin games. Also think of the mood of your game should give, it's joyful? It's terror of the abyss?