Good start to an arena shooter (with good potential for controller twin-stick support), with a good choice of sound effects.
Could definitely use some music, and the camera shake comes off pretty strong. I'd recommend reducing both the intensity and the duration.
I didn't get very far, what with having been caught off guard on a few occasions by an enemy spawning right on top of me. You might consider having enemies spawning off-screen, and jumping down the walls.
Points, or some other reward, perhaps to spend on upgrades between rounds (speed, fire rate, health), or power-ups for different firing modes would all be welcome additions to this good start of a game.
Well done so far, and good luck! :D