The game is good, although not all features are easy to understand for those who haven't read the description, such as feeding the altar. As for suggesting new features I think it'll be good to add:
"Use" button (Maybe default E or F) to interact with altar. Shooting at it can be a little confusing at start and I don't really understand how to level up at ninja, because when I try to hit the altar, nothing happens.
Speed kills. If you stumble upon an enemy at high speed, it'll send it into flight or kill it. Different enemies with different weight will require different speed of hit.
Keybind settings. Change binds (From walking at WASD to ESDF for example, or to bind shooting at mousewheel)
Restart button. Clicking RMB to go back to menu after death is really something that I understood only after drinking 100 grams of vodka, honestly.
"Back to main menu" or "Restart" or "Settings" options in pause menu (which opens when you hit escape).
Probably more maps or map progression, like some cave maps with narrow corridors that'll require player to move more carefully, after killing the final boss the ability to stay or go to the next map (Like in Soulstone Survivors).
Maybe reduce loading time after death, but that's not very critical now.
Also there are features that worked strangely in my experience:
Zapper. It's ammo was around -200, it seemed to work on it's own, like saying "Yo, player, you want me to shoot them for you? Hmm, let me think... Maybe this time I'll be so condescending to do that for you, but this is the last time, understood?". Quite unstable weapon at this moment, as well as the whole character.
Grenades. I don't have a smallest clue how they work. When you throw them, they can A: explode on the first time when touching the ground. B: Bounce off the ground and explode. C: Bounce off the enemy and not explode. D: Fly to Haiti for a vacation by bouncing off the ground multiple times and flying into ocean.
Damage boost/rocket jump. I don't quite understand how it works. One moment I can throw a grenade right under myself and it won't do anything in particular, but when I throw it a little further, it launches me into sky and turns me into a damn suicide Su-25 (Can't say A-10 because soldier lacks rate of fire).
Overall rate. Now the game is around 6.5/10 or 7/10. Nonetheless, I like the idea of the game ant the core gameplay is quite good. VOID has a great potential of growing into something much greater, maybe even a full Steam release, I believe in you, comrade.