Hilarious concept, and faaaabulous art!
I can't always get the "next level" to work. Usually I just get thrown back to the main menu. I got to the 2nd level once, but never again. I was on the web build and using Chrome, if that makes a difference.
I also found that I'm able to hit a button repeatedly while the move prompt passes through the "do it now" line, and points register for every time I press it. I felt I was cheating doing this, because I'm pretty sure it was intended to be like DDR, where you only get one chance to hit each key at the right time, and if you miss, you miss.
This may also just be me, but I perform better when I'm in two player mode (by myself), and looking at player 2's up/down/left/right prompts instead of player 1's w/a/s/d prompts. I tended to mess up with WASD prompts because to me, "D" registers as a middle finger key (because that's how I type in the ASDF position), but when my fingers are in a WASD position, middle finger lies W or S, and I press the wrong key. Derp!
I think this would go better for me if player 1's prompts were shown as ←↑↓→ as well, even if still triggered by WASD. This is more about tricking me into directional thinking, where "forward, back, left, and right" are more familiar concepts to my fingers from movement in FPS games.
Overall very nicely done, love the style, and that music really gets that monstrous work-out going!