Cool entry! I had fun and the shotgun mechanic is actually really smart! a weapon that is stronger if you hold your shot rather than spam is super smart and adds a really awesome choice throughout gameplay. I do think the game really needs a score/kill counter tho, there was very little reason to play long since I had no reference if I was doing better each run. The death animation on the enemies could also use a tweek, instead of a fade I think I would just having them vanish in a poof of particles.
But again awesome entry, the use of combined sprites was a awesome!