Cool use of the door! Art was simple but consistent in style. Lot of animations too.
There is no audio at all which makes it feel very empty.
I found the control scheme a bit odd. Why is clicking on the mouse the attack when mouse is not used for aiming or anything else? I think a keyboard only control scheme would fit the game better.
There also isn't any kind of score system. You're just surviving without any indication of how long you've survived, how many enemies you've killed etc. I think either a points/score system or a survival timer is a core part of a game like this.
Also on my monitor I couldn't see all of the tutorial text unless I put the game in fullscreen. You can see more or less of the text if you zoom in or out on the web page.
I feel like the major problems are things that are quite easy to fix, You've got lot of harder stuff down like the animations.