Very nice trowback game! I had so much fun playing this. I'm also working on my own game inspired by megaman legends, and seeing Delta gal gives me hope that, projects like ours, can show capcom that there's indeed interest in this series so we can finally play MML3 someday.
While I did enjoy everything, there's a couple of things I'd like to point out that could make this game even greather:
1- As people pointed out: the slide move is a bit counter intuitive to pul off. Dashing makes the character too fast and somethimes is a bit weird to get the timing to use the slide in thight spots. instead it could be used wen the character is sprinting but combining it with a crouching mechanic? So the sword atack and shooting could be performed while dashing and sprinting for a devastating combo. This would be a very interesting adition to delta-gal's (or Zeta gal, since I see you rebranded the game) already great moveset.
2 - The two main bosses are bees/hornets - This is just a nitpick of mine and I know this is a demo and I don't know your plans for the robots in your game, but it was a bit disapointing to fight a similar boss type twice in this demo ;/
3 - The secret boss - that worm drill... oh boy kkkk The weak spot was pretty obvious to see, but too annoying to hit lol The tight arena full of death wholes made fighting that thing simply not very fun ;/ I tryied a few times but I kept falling into the holes since I was to focused on the boss that closes in very fast to pay attention to them. And the pillars kept geting in the way and preventing me to hit him. I know it's a secret boss since you actually have to return to an area you already cleared to fight him, but the tight arena + holes + pillars + weakspot on the back + movement speed combo was a bit overkill lol Removing one of the hazards or slowing the drill a bit could drasctically improve the player's experience for this fight, or making the drill get stuck for a bit after an attack.
I know you'll not update this demo, but if my tips could help a bit your design for the final game, then I'm happy. As a fellow MML fan who misses this games greatly, I'm very glad I'm not the only one trying to keep this series spirit alive.