Interesting idea, but I see a lot that can be improved here: 1) an option to replay the game without having to reload the browser page every time would be nice. 2) your pixel art is blurred. If this isn't intended, then you might want to use the texture filter nearest and not bliniear. 3) A better font can improve your game (there are lots of free fonts on the internet) 4) I think I found a bug: When you die, it says "seconds until death" followed by a negative number, which I think shouldn't be the case... 5) The game has no sound effects. Sound effects can also improve the game's feel by a lot. 6) The background is just pitch black, I think a castle-like/ brick background or sth like that can help to set the scene.
I hope these aspects will help you with your future games