More little polishments would be nice to get a good feel. For example when shooting the boss it doesn't really feel very satisfying, more particles, such as bullets impacting the enemy, and a sound effect when hitting the enemy. Some death particles would be good too. A visual effect, maybe like a flicker, or a shake. That'll make you really feel like your hitting it 👌
Some camera shakes can also feel impactful, though they would be more for the player. You could probably have a good use of the unity trail renderer, like adding them to bullets maybe(Though just a personal opinion since I love how that looks).
Good luck on your game, I'm sure you'll do well!