Good concept!
Here are some ways I think you can improve the game:
- Start menu should be more colourful: even a still image beats a black screen
- Add clickable button alternatives for some keybinds; it was hard for me, a new player, to remember all of them. You could also have a “controls” infobox on screen instead of putting them in a menu sidebar.
- Perhaps make the skybox more interesting, or add some terrain features