Original, and the mechanic was cool when I figured it out, but you need to do something special with it. Like, maybe there's a level where you can't really keep your horizontal velocity zero because of wind, or something. Weird things and implications that don't matter in most games but suddenly make a world of difference in yours. Make me care about the gimmick!
I crashed upon taking damage, possibly lethal, in the second level with the burst fire army guys.
Oh, I really like that idea! I personally thought of linking more different statistics originally, like constraining an enemy to a certain height based on for example your health, something like that.
As for the bug, it's a known one and is fixed already in the fixed version of the game I linked in the description, that was caused due to the game over screen referencing the wrong background (two levels always share the same background, so the background ID is half of the level ID rounded down; and the game over screen tried the level ID directly); which you can actively see when dying to the mad scientist (level 2).
