This is some very helpful and constructive feedback.
Starting with the direction the arrows go in, we thought about if for quote some time, with the original idea being that the sequences were shown horizontally and go left to right, but it made more sense in the screenspace to have it vertical. Because of this we added the animations where the arrows bounce slightly when they activate to sort of force the player to pick up on it.
As for the grid representation, we have considered that idea, but it sort of goes against part of the steps of the game. It is up to the player to parse the sequence and build a mental grid themselves and then see where that pattern would fit in given their surroundings.
The gray dots! Those show you what tiles would have been okay to stand on in order to not die during the next sequence. Apologies if that was a little unclear. We are working on adding easier levels and maybe their purpose will be made more obvious on a smaller grid.
There actually is a fullscreen! Since we are wrapping the game with a minified Chromium window, you can press F11 to fullscreen the game and it should work like how your standard browser would fullscreen. If you are having issues with that let us know so we can look into it.
Different screenshake levels. That is a good idea. I'm pretty sure we thought about it at some point in development but it never made its way onto the planning board, so thank you for the reminder :) We will most likely split the current setting for screenshake into two separate booleans for screenshake on move and screenshake on "bonk."
Hope these responses were inciteful, and I look forward to seeing how both of our games progress with time :)