So I played for a bit and had a number of ideas which might be interesting to you as some ideas how to improve the game. I don't expect you to want to pour more time and energy (and thereby money) into this project. I wouldn't expect these things to be "worth it" except as a learning experience.

Small QOL (quality of life) additions:

1. The menu could be a bit more clear by highlighting the selected element/entry/option with a different color in addition to brackets and description. Right now I can easily lose track of where I am with the text-cursor for a second.

2. It would be nice if the menu could be navigated with all keys that can be used for playing as well. So if one is playing with IJKL or WASD, they don't need to move their fingers. This would also apply to the firing key being used for selecting options instead of Enter.

3. Similarly it would be nice if when playing using a gamepad, the player doesn't need to take a keyboard to navigate the menu. Again with the firing key for selecting stuff for example. Or follow the convention of (using Xbox and Steam Controller terminology) A for select and B for back. Those are the bottom and right button respectively over where the thumb is.

4. For the previous addition, it would also be nice if the game could be paused (exactly same as Escape key during game) with the start button on gamepad.

Less important additions:

5. A small improvement would also be if when the player holds the Down or the Up key in the menu the selection keeps on moving while the key held down (until it reaches the last selectable item). Currently when I hold the Down key it only moves down by one element (since it moves down once per key press, not once per 0.6 seconds while key is pressed).

6. Personally, I would find it more convenient if when playing using a gamepad shooting and acceleration would be the lower buttons. That is (using again Xbox terminology) Left Trigger and Right Trigger instead of Left Button and Right Button. Since I assume different people would like different things, remapping would be a nice feature, but I understand that would be a lot of work and I can work around it with both Steam client remapping options or with an open-source remapping tool for Linux by Kozec.

7. Personally, I would find it easier if when playing using a gamepad, acceleration would be separate from turning. I would like to turn without being able to accidentally accelerate with the same button/joystick. Hypothetically there could be a toggleable option for this in the settings menu.

Thank you for the feedback! I think some of these are already there in some form, they just might need some tweaking:

1. I haven't seen this as a problem, but it shouldn't be too hard to make the highlight more visible. Added to my todo -list.

2. I have intentionally limited the menu control to certain players to prevent "menu fighting" as multiple players try to navigate in menus at the same time, either accidentally or intentionally. For keyboard, it's the rightmost player as arrow keys/enter is the logical choice for menu controls. Selecting should work with that player's fire buttons (right shift/ctrl) too.

3, 4. You should be able to navigate the menu using the first gamepad's dpad buttons and X/A button. The menu and controller help overlay should toggle by select/guide and start -buttons. Does this not work?

5. This is already on my todo -list (as low priority item, though).

6. The reason for not using  the "triggers" is that depending on gamepad they can be digital buttons, analog triggers or completely missing. One set (the upper on XBox/PS controllers) of trigger buttons is (almost) always present and digital. 

The controller remapping question comes up often, but it's unlikely that I would add that. I have instead tried to add alternative buttons for things that annoy people the most. The reasoning is that this is supposed to be a party game where players change often. If the controls could be changed, most of  the time would be spend in menus tweaking  controller settings instead of playing.

7. I'm not sure if I understood the problem.. Right stick only turns without accelerating.