Of course, I will try to describe, but keep in mind it is just my opinion, you don't have to change anything because of it :)
First, the shape. The surroundings are all sharp corner walls, but the player is all smooth and roundy, no corners, no sharpness. (I also saw your reply to Speed576 and an example of an enemy - also looking sharpey! I like that design!)
Then the colors. I am not an artist, so again take it with a grain of salt, but the surroundings are black and green and look cold, and the player is very bright and warm. It is understandable that the attention should be on the player character, so they should stand out, but maybe you could find some balance between capturing attention with character's looks and make it more in harmony with surrounding level.
My suggestions to improve this would be to change player's graphics. Maybe make a robot instead of astronaut (sharp lines and corners) and change color to something colder and more subdued (Maybe violet? Just a suggestion though).
Or change the level style to fit player character, but I like this option much less (also the music really fits the surrounding. If one of it changes, the other probably shall as well).
Hope this helps! (And again, this is my personal opinion, and I might be objectively wrong here)
Looking forward to seeing how you develop it further!