I'm very impressed with your demo! I believe you were going for the Megaman Legends look and you nailed it! The music was good as well!
I only noticed a single bug that effected the demo: sometime the turret would get "stuck" and wouldn't rotate towards where the camera was facing, but other than that everything seemed fine to me.
I only have a couple gameplay suggestion: it'd be nice if you could add a spatial sound-effect to the enemy boats or projectiles, that way the player could keep track of his surroundings without having to pan the camera all over the place (especially since the turret tracks along with the camera). Also, I think the enemy drops should vanish after an amount of time--if you watch the footage I attached I ended up just going around the perimeter of the maps kiting all the enemies into one big death ball--with the time limit maybe it'd incentivize charging in to get the drops. Other than that gameplay seems solid to me--I liked the health boats & think they're a cool idea.
Here's my footage & I hope it helps. Took me about halfway through to grok the game but I enjoyed it!