Great and fun game. Maybe create a patreon and accept donations to keep this game (and maybe future games) free? Also I'll add a lists of things to add.
1. Cosmetics like hats, taunts etc. something kind of like TF2! I'd be pretty interested to see these blocky faceless characters have hats and taunts. It's like they're made for them!
2. Multiplayer. This might come in version 1.0, when the game has developed more.
3. Levelling up. Maybe add different levels which would allow you to get better cosmetics, armour, skins etc. kind of like CS:GO.
4. Crates. Crates aren't a CS:GO only thing. Maybe you can earn a crate every level up? Who knows. These crates could have skins, hats, taunts and more.
5. Some diverse maps. From a desert to islands to a jungle, it would be nice to have different terrains and different vehicles for them.