I like it!
Played it with a trackpad (can't aim and move at the same time) which added a bit of extra external difficulty. I really like how much the game penalizes you for walking backwards.
Despite being in control of when I got a wave of enemies (after I got regen I was basically immortal by playing like a coward), it still maintained the feeling of danger when leaving the safe zone. The quick and unpredictable spawn rate really keeps you on your toes.
Gotta congratulate you as well for making it without an engine. I wouldn't have guessed from the look and feel of it.