First, loved the movement feel. I like the graphics, the style, and the music. I like the power of certain shots and I liked being able to choose my upgrades.
Just in the form of suggestions, I'd like to say to help situational awareness you might want a stronger spawn sound effect (possibly with surround so players can tell where enemies are coming from) and sound effects for each creature. The gun sound effects could be a little better, and I felt that the axe was woefully underpowered. The double jump felt great, although it fell short in a lot of places that seemed to be in reach. Finally, I think as a whole it's annoying when you're firing enemies and when you kill one, their death animation takes bullets for the guys behind them. Especially with the ice creatures.
The biggest problem was probably the fact that the skill names and weapons were either variables or placeholders. Great demo though, I hope to see good things from this!