Couple feedback points: I really hate the health system. I wish it was clearer how much health the potion recovered. I'd almost have it more like a traditional unit-like health bar and the potions recover one unit. Also having the R key so close to the movement keys made me press it in a panic several times when trying to move away. ALso allowing you to use a potion when your health is full feels really cheap. Also what about purchasing such items in the store after each level?
I never really got used to the strict 90 degrees movement and my fingers constantly got confused between strafe and turn. But I'm sure I'd get used to it in time. I'm more used to the FPS movement when this is more of an arcade-style setup.
For the map, I'd recommend holding the TAB key to show it, so it's just for quick glances.
Would have appreciated a little more variety in the props, though I only played to level 8, so I'm sure more gets introduced. There were new enemy types all the time which was nice.