The shooting is fun. As Steventus said, more gameplay-changing powerups would be good. In a lot of survivor games, they increase the player's arsenal with a lot of weapons/ability powerups. That goes a long way towards making each build/run unique.
I think the art assets are fine but the color theme lacks contrast. I haven't played devil daggers but it has red accents on black enemies which contrasts a lot. Here the floor is blue. The hittable parts of the enemy is blue. The transparent red body makes it even harder to see. I would suggest rethinking the color scheme here.
Trance music is a great choice for a survivors like game as they tend to be "zone-out" games. With some more SFX it would improve a lot.
Overall, it's a fun entry. As a programmer, I totally understand the pain that is art. Picking a good color palette can help a lot in that regard.