Very nice submission! The art for the ships, especially for the boss, was outstanding! It had a great oldschool arcade-game feel and I played for quite a while. Simple but addicting gameplay.
I think the difficulty could be adjusted to make it easier for the player. Some common tricks are just to make the hit box smaller than the actual size of the ship - even though it's less realistic it will make the player feel better. And for the sound effects, a trick I like to use is randomly scaling the pitch every time a noise is played if there is a noise played very frequently. Also I'm not sure exactly what the RES bar was for in this game, maybe I didn't use all the tools I had available to me but it didn't seem to go up or down.
Overall a great game for the short jam. Nice work!