I like the art and the overall atmosphere, especially with the shadows in the background and the fog that creates a feeling there's something hidden behind, like monsters, love it! The sound also helps a lot to create this mood, and I liked the SFX's too.
About the gameplay, I struggled a bit at first to get used to using space + RMB, but once I understood it, I was able to make progress and it became quite easy. I also liked the effect when your energy runs out, it gives off a strange, eerie sensation. At the start, it was fun to kill enemies, but after a while, I realized I could just go downward and avoid them entirely, as they didn't seem able to damage the ship from behind.
Overall, it looks great and creates a strong, immersive atmosphere. Nice work!