The game is already pretty fun.
In terms of difficulty, the combat feels very hectic but I managed to beat the entire demo without losing a single life. I essentially kept almost dying over and over.
Bomb spam is very strong, like in a game by Psikyo.
By comparison, strafing doesn't feel particularly useful.
I think the game could be really good if it had more enemy types and more interesting upgrades besides flat stat increases. The familiar that eats bullets is a good example of an interesting upgrade.
Keep up the good work.