Good foundation, got a couple big problems. There's not delay between enemy shots, so they're just shooting a constant stream of bullets and if you ever get hit, you're instantly dead. Neither the enemies nor the bullets rotate, so the enemies are shooting the bullets sideways out the backs of their heads. And the bullets don't despawn, so once you've killed the 5 enemies, there's just a hanging taffy rope of floating bullets all around the arena.
Other than that, though, it's pretty good. Little slidey and there's no sound, but whatever. I like the enemy design and having the ammo counter change to ". . . . . " while you reload is a really cool touch. All it's missing is a title screen and a "You Win!" popup after you kill the last enemy. Good job!