Your game is easy to understand, demonstrates an interesting game mechanic, and is straight to the point. If you build out that game mechanic just a little more, you could create a fantastic game.
So the character is your average joe, then you hold down the space button. He becomes a devil that charges forward and attacks anything that breathes. I can think of several hazards and challenges that could work great with this human/beast mix. Complex mind button challenges, conversation challenges with certain NPCs, simple platforming, and some timed challenges.
Now for the beast, you focus on brutish type challenges that happen right in the mix of the human difficulties; that is where the fun happens. You have to quickly switch between those two modes to deal with the problems at hand. You can also create another trait for the beast, restrict vision. This trait will make it harder to plan and force the player to deal with the challenges quicker.
You did a good job, my friend! Keep up the good work!