-You need borderless fullscreen mode or borderless windowed mode. A way to run the game to cover the entire screen but with much easier alt-tabbing. Many people have multiple monitors and this also allows them to multi-task easier. In addition it is easier to stream in such a mode compared to the fullscreen-exclusive mode already present in the demo.
-No customizable controls is really crappy IMHO, however I hope this can be worked on for the full version. This isn't some RPGMaker game which requires special custom scripting to rebind keys. So act like an actual game and allow gamers to customize their control scheme please!
-Even at 50% volume or lower, the music seems REALLY loud but that may just be my setup. May want to consider starting the game with all volumes at about 50% of normal volume; let the end-user choose to adjust the volume if needed.
-Bit of a nitpick but screen shake is a mere toggle instead of a gradiant slider with 'more' or 'less' options. Minor QoL thing if this could be improved upon for the final release.
-Another nitpick but the severe lack of resolution options is disheartening and concerning. I get the whole 'but da art style' which is fine; however I've seen many other pixel art games like Hollow Knight run perfectly well in a wide variety of resolutions. There is no valid reasonable excuse for why the resolution options shouldn't be 'anything the monitor/gpu/os can support'.
-Yet another minor nitpick, but I'm not a fan of the black bars and would prefer to see more of the environment.
-The very first enemy encountered that shoots ranged projectiles will hit the player at least once (maybe twice) before the player can become accustomed to the dodge roll mechanic. I strongly feel that this is poor game level design and a simple look at Megaman X (or the NES originals) would show how to do tutorialized level design without punitive split-second punishment of the player. I'd recommend a lowered ledge on the initial approach so the player has a chance to practice dodge rolling in safety BEFORE hopping up the ledge and trying to get past the enemy. Not everyone is familiar with 'iframes' also and therefore that should be communicated in some fashion.
-Why isn't the player taught about ducking? Not every game allows ducking and many potential players may not know about it. It also isn't listed anywhere in the control options (only 'movement' is listed). In fact, best way to deal with those plant enemies is by ducking.
I love the audiovisual design and aesthetics. I look forward to the full release! :)