Thanks for trying the demo!
I will try to balance the need for tutorials better in the full game - I’m almost considering a sort of “training” room you can access from the menu for the very basic stuff - experienced players can ignore it, that way.
And yeah, I am evaluating vertical firing along with adding a crouch. Whether it’s done by allowing aiming or via an alternative weapon, you will eventually have more options in combat.
A preview option on the chameleon circuit is a good idea, and yes, it should be doable. I’ll be reworking the menus for the full game and I’ll try to incorporate that sort of affordance wherever I have an option like that.
The issue where you sometimes drop down quickly is a real one and known. It’s been surprisingly hard to track down, but it’s on the list and will be fixed.
As to your final issue - I have an Everdrive X3 and it saves on that, though I have to press the button in the cartridge to go back to the menu for it to persist - if I shut the gameboy off it just disappears.