This was a fun gameplay concept! I know with game jams, sometimes all you have time to do is get the core mechanic working, and I actually think you were able to get it across and it's pretty solid! Moving the ship, aiming the cannon, and finding the right timing for the "ghost mode" all felt pretty good, and the enemy AI had a nice arcadey feel.
I tried the browser version both on mobile and desktop, and I have to say I found the controls a little hard to use on both. I think the biggest issue was the clickable area for aiming the cannon. It would be a huge improvement to be able to click (or touch, for mobile) anywhere on screen and have the aiming guide come up, instead of limiting to only the immediate area around the cannon. Also, on mobile, the way I hold my phone, I think I would have preferred the movement buttons to be stacked vertically instead of side by side, or maybe a virtual joystick so I could slide my thumb left/right.
I will admit, I didn't make it to the end of the game, but I see a lot of potential to develop this idea! Maybe one possible future improvement would be to make it so there are ways to earn power ups with well-placed cannon fire or other things, so it's not just the one tiny health boost after every encounter. I know it's hard to get those kinds of balancing issues right in a short time, though.
You did a great job of creating the pirate "feel" with the dialogue in the intro and the music. I also really liked the sprites for the ships, but perhaps the background art could use some sprucing up. Maybe some clouds? Even just less chunky pixels to better match the scale of the ships might help keep things more visually coherent.
Overall, nice idea for the "legends" theme and cool gameplay!