The environment is really nice - the graphics is very well made and everything fits together so well and the sounds just add to the great athmosphere :)
What was a little bit annoying is death that you can only hardly escape - once I lost 2 hearths right after spawning and sometimes I felt there were too many thigs coming out of my screen that just killed me (out of nowhere a laser! :D )
And after I have developed some simple strategy (going inside walls, getting a flamethrower and shooting from just narrow path, I felt like I could just sit there forever and get as high score as I would like to - I feel some motivation to move and go somewhere actually would be really great :)
Overall really nice job, I think that with just a few changes it could be really great game with quite a long gameplay :)