|Greetings from the Critique Club
I must say I was rather expecting to see a lot of firework images in July Free Study given the recent holidays in North America.
I know fireworks are incredibly difficult to shoot well, I have tried only once and gave up as i was getting nowhere, so kudos to you for persevering.
To score highly in a Free Study with a firework image, the technical aspects need to be completely spot on. In the case of this image, the technicals are lacking a bit which is why I think you ended up with a 5.3.
Typically a low ISO setting (say 100), small aperture (High F number) and slowish shutter speed will give you a crisp clear image (of course, using a tripod). The settings you have used tend to leave the image quite blurry and thus the impact is lost. So, from a technical point of view, I think you image is suffering a bit. The fireworks are blown out in places and are quite blurry.
Mostly I think it takes a bit of practice to get good firework images, but the opportunity to shoot them doesn't present itself too often.