Liked it so far, cool overall style, and the sound design together with the weird and distorted enemies make it pretty eerie.
The idea of the locked doors making an error sound is really cool! How has this been achieved?
Things I didn't like that much: There are black blocks all around the sprites, was this on purpose (to catch a certain style of the ZX Spectrum maybe?) or are those JPG artifacts or something? Also doing basically the same level over and over again is a little bit boring, and I didn't find the key in level 3 so far...