First of all, congratulations! It's a great demo. I can feel how much effort you have invested in developing the game.
I really like the graphics and the control. I feel nervous when the enemies are approaching me. Awesome!
On the other hand, let me say that experience gauge increase speed is not rewarding at all. It moves reeeeeealy slow. It seems that I'm in level 50 already. It should increase faster at the beginning. Maybe it's just a demo and you set this speed on purpose.
All and all, I love it. Keep up the good work.
Edit: I forgot to mention that I love how the dog (rat?) collects the diamonds.