Love the visuals and how it pays homage to old school FPS. I don't play much of this genre to know if it plays like those games, but I definitely think you've nailed the style here!
I do wish there is a little more feedback effect when enemies are hit. Maybe just a sprite flash or some overlay hit sprites when my shot lands. It'll make the gameplay feels a little more satisfying.
Also, I think ammo should respawn if ammo is essential to complete a level. Shiori's stage kinda locked me out when I completely ran out of ammo (I only found out partway through that you are supposed to shoot her when she prepares an attack). Either that, or there should be an alternate way to perform attacks without locking the player out when ammo runs out. (maybe like a melee attack that reflects her projectile etc)
Good job overall though! Thanks for making this!