Thanks for the suggestions, I will definitely work on adjusting the learning curve and limiting axis is a great idea!
About the keyboard type - it might make a difference if you have a keyboard that doesn't register too many keys at once (like some membrane keyboards do) when you spam keys. Other than that, it shouldn't make any difference, as the game just takes in your binary (on/off) input and adds/remove velocity in that axis.
On the same note though, I have implemented today an adjustable setting for torque multiplier, which you can adjust for either more (chaotic) power in your keystrokes, or less power with more control over your movements. That bugged me for a long time, cause the game runs differently in Unity Editor and differently when built... now you can at least adjust the settings on the fly in the built version too.
Thanks for playing the game!