The how to play screen is helpful but the text is a bit small and hard to read in options and upgrade menus.
Maybe an reward for combo-ing the obsidian and encouraging the player to not let it touch the ground would make it more fun
Upgrades like multiple obsidians/weapons will also increase the interactions of the game
the player being unable to control his jump height means that he has no reliable way to dodge the late game bullet barrage other then praying he kills things fast enough(or rely on hp regen also)
having an enemy that hides at the top and spawns a power up on death would encourage the player to make trickshots with the obsidian instead of just smashing it into enemy groups,which increases the skill ceiling
the game froze also the gun sfx is pretty loud