Almost perfect.
Everyone who follows your work for any amount of time will notice you have been working on 'figuring out' adapting run'n'gun formula for modern design for a long while now. Jet Gunner, Sole Gunner, Alien Splatter, Steam Heart - each of them an interesting experiment, but each of them was missing something.
I think ironically, due to having to abide by theme of Ludum Dare contest, you have actually figured it out.
The thing that was missing, the thing that everyone loved about Contra and Gunstar Heroes - speed and flow.
I think this is your best game so far. And I'm dead honest here. It's amazing. Definitely your best work so far. Oh, it's flawed, definitely, for sure.
Game on my computer runs with a terrible slowdown and while it's pretty old, it runs other indie games without a problem - including Freedom Planet which is a *standalone Windows* genesis-like. Controls are a bit wonky. Some weapons like Fire are almos useless and relatively hard to avoid. Explosions and flicker combined with slowdown sometimes make it impossible to understand what's going on, and you can damage a boss when they're offscreen and in a "Warning!" (maybe this was issue with Missile weapon I was using?)
But the thing is, those things can be fixed. Underlying design, of a Sonic-like speedrunning game where your timer is your health meaning that mistakes are perfectly forgivable without making game easy, the satisfying dash mechanic that cancels enemy bullets, the interesting and wacky enemy design that remind me of Noitu Love or WayForward games, the controls that don't need more than 3 main buttons, mixing - it's all great.
I'm giving 4.5/10 because it's the last grade below perfect, but consider it more of a 10 but needs polish/10; It's definitely the single most satisfying game you have made so far, and I liked your old games a lot.