Very cool demo so far! Lots of Metroid Fusion vibes. One thing that stuck out to me is the damage flash that enemies recieve when getting hit. When damaged, they turn white and fade back to their original sprite quickly. If you hit them while the white is fading, there is no visual inidication that they're taking damage. Because of this, I ended up going through most of the demo thinking that attacking enemies too fast meant that only half my hits were doing damage. To solve this, simply make it so the damage flash can restart if it is still fading out.
Also, the Sector 3 boss is kind of buggy. The conveyor belt just makes you go faster instead of pulling the playing in a direction, while the normal floor in front of the left doorway has the behavior of a working conveyor belt. The boss itself will freeze in the middle of its animations and the music will stop looping when it reaches 1 health. I can provide video of this if you'd like.
Overall the experience was pretty good! I especially like the ability to sequence break Sector 1 to get the shield ability early. I look forward to future developments.