This is a really good start - you have good core gameplay mechanics movement is good (I like slowing down when the shield is raised; it make me feel heavier) and the knock-back is perfect. I also like the limited visibility. I especially like that WASD are linked to the direction of the mouse. That gives it a really unique feel.
I'm trying to think of how to turn these basic mechanics into a compelling game. I think a top-down fantasy survival horror with limited resources could be fun. A side-scrolling platformer has certain advantages that a top-down game doesn’t, but with the visibility feature, I think you could make it work.
Since this is a melee game, weapon variety will be important. You'll have to make sure each weapon feels very different (play Dead Cells for some great ideas). I like Halo's limitation of only 2 weapons at a time (with extra items like grenades, as well). Weapon attacks should be tied to movement as well - swinging a mace could push your player back slightly, or thrusting with a spear could move you forward.
I think weapons with limited durability (like Zelda BOTW) would be really cool in this context. The gameplay loop would be attacking enemies until your weapons’ durability is gone (like running out of ammo) and then scrambling to pick up a weapon from a fallen enemy to keep fighting. To add diversity of pacing, you could mix in exploration portions so it’s not just constant combat. I wouldn't put in an inventory screen - you shouldn't be able to pause this game or get out of the setting.
You might consider having the shield be slightly off-center – that way, players would have to aim somewhat in order to block properly (or attack a defending enemy).
Armor will be the other main consideration. Heavy armor could reduce your visibility but prevent you from being knocked back, or magical armor could damage enemies at a distance.
Exploration is what I'm most interested in, though. You could use visibility as a way of searching - secrets (like trap triggers, hidden enemies, treasure, hidden doors, etc.) only get revealed when you've had the lighted part on them for a certain amount of time, so the player has a reason to take it slow sometimes. Some enemies could appear like one creature (or item) but then be revealed in their true form once you've searched them enough.
As for a "story," I always wanted to make a slave revolt game. You could start as a gladiator slave, but escape through a dungeon. You’re really vulnerable at first, but then you find an item that lets you absorb enemy powers. Then you as you slay monsters, you gain their abilities (like in Metroid, but more gradually), and then return to kill all of the slavers. Maybe you could even have monster allies that could fight with you sometimes.
Enemy design will be interesting, too. I think some enemies should work in groups with different kinds of group dynamics. There can be large swarms of weak enemies, or medium groups of weak enemies with a leader that buffs them with spells in the back, or packs of high-mobility enemies that attack from different sides, or just one really slow, high-HP enemy. Some enemies should hide until they’re ready to strike, and then leap out for a lot of damage, and then try to hide again (having good environmental design would be good for this). Certain enemy types can have a lot of treasure, so players really want to fight them, while others never have good treasure, so players try to avoid them.
I imagine enemies with different weights (some get knocked back really far, and others don't move). Like in Dead Cells or Dark Souls, each enemy should have a specific attack motion, as well. That way players can try to predict what’s coming and time their defense and counter-attack.
I really like games – I almost went into game design. Let me know if you want to brainstorm enemy design or levels. Thanks!
