Reminds me of nuclear throne though i never played that game, haha.
This was pretty good! The art is really nice and the mechanic, though not very original, is well implemented. Simple and nice!
From the mechanics side, it needs a little bit of complexity, IMO. A enter the gungeon/nuclear throny roll would be quite nice, as would be powerups that could spawn around in the map just to make you move more around. Maybe even traps on the floor, or holes. You could even lead enemies to them!
It was weird for me to see the enemie's life, as i thought most died in a single hit so what did it matter. Later i figured out it depends with the force of the throw, however you must barely hold to make 1 damage. Would probably suggest having to hold it more, and maybe adding some more punch to the throw.
From the graphics and feel side, graphics are nice, but it really needs better feel. Screen shake when enemies die would be awesome, specially coupled with particles that could fly off them if you kill them. Coupled with a sound of the spear ripping through the monster and if you land a good multiple hit it would feel incredible, with particles flying everywhere, monster parts on the floor and screenshake going wild, while hearing the sound multiple times. It would really change everything!
Sorry for just posting mostly ideas in the comment, i just see this as a game with really good potential. Continue it!