Not a bad start. There is definite promise here. A couple points I'd make are the momentum needs to be tweaked and turned way down if you intend to have any sort of precision platforming involved. I was able to clear the first section of simple jump after numerous failed attempts - the acceleration and max speed are too high, and any success comes more from chance than skill.
Second, Keyboard/mouse inputs are likely to be the most common, as this is on PC. It would be very helpful to make sure they work, and players don't have to figure them out by pressing every key to see if something works. I found WASD for movement, Left Alt for stomp, Left Shift for duck, and Space for jump. Couldn't seem to attack at all, despite trying literally every key/mouse button. It would absolutely be a good idea to make the controls work across both hands, as right now everything is done with the left side of the keyboard
What's there in terms of spritework is good so far, though in later builds the tileset for the map could use some work, so it's less of an infinite world of cubes. Also, at the end of the stage, there's what appears to be a blue door. Couldn't seem to interact with it, but that could be down to a seemingly missing keybind.