Sorry, I was just passing through and know nothing about the game, but players who get motion sickness very easily _will_ appreciate the 'screenshake toggle' greatly. No matter if it's 2D or 3D, if you get it bad enough, it will bar you from playing certain games.
I'd view that as a critical feature.
Personally, I view the option to mute/control the volume for BGM & SFX within the game as standard features. No matter how beautifully you manage to incorporate the audio into the gaming experience, 'somebody' will always prefer their own music or a podcast.
Maybe not a "critical" feature, but personally I'd 'expect' it to be there in anything that isn't a single level tech demo.
Remi-le-Oduen
None of those feel really critical to me