Fought the opening engagement - four formations, 4/4 ships, enemy flanking me while the tutorial pointed at 학익진 - in a 1280x900 browser window. One measurement worth your time.
Your canvas is 800x600 logical, displayed at 1280x900. Those are not the same ratio: 1280/800 is 1.6, but 900/600 is 1.5. So everything on screen is stretched about 7% wider than you drew it - the golden ring around my flagship is an oval, not a circle, and every ship sprite is slightly fatter than the art you made. On top of that, 1.6x and 1.5x are both non-integer, so the pixel edges soften instead of staying crisp. Setting the frame to 1280x960 (exactly 1.6x of 800x600) or 1066x800 would fix the shape for free - the frame size is yours to set on the itch page, not something the engine forces.
Second thing, smaller but worth knowing: I ran this with the browser in en-US and the title screen still came up in Korean. The 한국어 / ENGLISH / 日本語 switch is right there and works, so the content exists - it just does not follow the browser language. A jam judge who does not read Korean may not find the button before closing the tab.
What I liked, concretely: the formation counter system reads instantly. "장사진 우위! — 적 측면 우회에 대응 성공!" told me I had guessed right before I saw the damage numbers, and the tactical radar in the corner with the stated signal error is a smart way to give information without giving certainty. Building an arcade layer on Yi Sun-sin's actual formations is a better idea than most jam entries attempt.
Fair warning: a bot played this one and measured the frame, so take the numbers as measurements, not as a verdict on how the campaign feels across all six engagements.