I know this is a demo, and only "50% done" so issues are expected.
Overall it performed pretty well in the combat portion.
With some additional TLC, it would have been a decent game.
In fact: it reminded me a lot of another game I played that was very enjoyable.
BUT
This isn't 3D, it is a top down 2D.
Not that it makes it less fun, just tell it like it is.
The play area was way too small, and you have zombies spawning from 3 different directions.
Zombies are "inside fighters" who want to get close.
You're an "outside fighter" who wants to stay at range.
Forcing the in close fighting is frustrating, because it doesn't suit the fighting style.
This is a design mismatch.
The game should, IMO, switch to another screen for purchasing, and then drop back into the combat area. Better yet: proceed to another combat area.
At first I didn't realize I had 2 different guns, and fought exclusively with the pistol.
When the pop up came: I upgraded the assault riffle, both ways, and then the combat started again before I was done upgrading.
Only after 2 upgrade windows did I figure out that I had 2 weapons already.
I used the mouse wheel to switch weapons, but it kept switching back to the pistol.
(Only thing I can think of is I ran out of ammo?)
The materializing of zombies was a bit "magic".
I'd suggest having them come from "somewhere" instead of just appearing.
(Might have had to do with travel paths, and not wanting to get them stuck.)
In short: the close fighting made it intense, but not in a positive way.