Good; But easy.
It's a decent build with what you have so far. The biggest issue is how easy the game becomes after level 10 or so.
-The Stamina upgrade doesn't seem all that useful.
-The game has way to many 'Free' zones; By this I mean the zombies will walk right past you and into the center of the room before they aggro on you so to speak if you're standing at the corner of any of the door ways. Most noticeable is standing on the right side of the bottom left door.
-The elevator music between the levels was good but felt it could have switched up between two or three different songs and maybe being able to do a bit more with the levels or some sort of system to unlock additional content.
-The backgrounds get boring after awhile given it's only like three or four on rotation.
-Topping the high score is really about how much patience you have. Since you give three lives and even level one of Stamina is fast regeneration.
A rating of 7 of 10 or 4 of 5. I liked it; but feel it could be polished.