Congrats on Your work
I find survival mode very addicting. Your game is awesome and I hope You will finish it. I believe some stuff could be tweaked bit more.
I die two-three times very fast and than I learn that constant moving and shooting is key to long live
game could be bit more hard with additional gun parameter like range. I would love to see also more gun power levels. I think game could start with even bit lower level of gun power. That feeling when group of those slime/ghost follow You and You are constant shooting is great.
Another idea is to introduce more money items - like silver coin that gives player 1$, golden coin = 2$, gem =5$, very rare gem =10$.
Also more colorful ghost
, maybe special ghost types that can do different stuff. Ghost that can teleport, become invisible for short amount of time, heavy armor ghost, ghost that split into two smaller ghosts when shoot