Quite fun! I like the music which really sets the tone of the game and the pace of the game follows it quite well.
I found picking up the dead slime a bit of a chore, because you do kill a lot of them and there's no auto pickup. I think if you still want the player to have to get close to the slime "bodies" to score points, you could make the player's movement speed a bit higher and/or implement a proximity auto-picker so you don't have to go exactly to the position of the body.
The different slimes where a nice touch, though I didn't find them to be substantially too different when playing. I think the dashing slimes could be a lot faster to pose a bigger threat, and the mother slime have much more life to make it tougher to kill.
Beyond that though I really liked playing the game! The subtle camera shake when shooting is a nice touch - again helps with the whole frenetic feel/pace of the game.