Lovely graphics, nice sound. Very impressive control set--crouching fire, diagonal fire, etc. Everything seems to work smoothly. Effective (standard Metroid-style) minimap.
The variety of enemies, each with its own behavior, is also impressive. "Game juice" is well implemented, with flashing, knockback effects, etc.
The choice to omit auto save seems a bit unfortunate. Having to schlep back and forth to perform a manual save is a bit of a chore, without much added gameplay value.
Also, the setting suggests a story... I would love to know more about what is going on here.