I really like this! I like the concept and the animation on the astronaut especially. The floaty jump and the heat haze effects were also great. I also like the way the dinosaur type creatures jump at you when they have the height advantage (presumably a way of getting them down slopes without issues but nevertheless very cool).
I like difficult games although I couldn't get through the second area - those spinning things! The frequency and range of these creatures combined with the fact they bounce you out of the way made this area frustrating.
I have just one suggestion would make this easier to play through without compromising too much of the game's difficulty. When I had an enemy coming at me, my instinct was to back off and shoot, but this actually just makes me aim upwards. Perhaps you could have the ability to walk backwards while still facing the direction in which you're aiming? If your design would allow for this then I think it may make the game that little more playable and accessible.
Anyway, keep up the good work and I'll keep trying to beat that second area!