Awesome concept. I like the powerful feeling after resurrecting dozens of skeletons into my army. To my taste the movement was a bit slow and the boss could have used a health bar. The game has great sound design and atmosphere.
Have you tried using "E" button? It was in the tutorial part and should give you x2 the speed for 3 seconds for just a quarter of your energy bar.
And nice idea on the health bar for the boss, I wonder why I never thought of that before?
Oh, somehow I missed that speed boost in the tutorial stage. Thanks for the tip.