Great game, definitely has a nice and retro feel to it.
I enjoy the movement of the game, it's very different from what you usually get with these types of games where it's mostly instantaneous movement - the addition of acceleration makes it stand out well.
I do think the difficulty curve is a little bit flat though. Since the game goes on forever, it would be nice to have it scale so that the player eventually loses at some point, I played for 10 minutes and I could probably go on forever if I wanted to.
The art is nice, the design on the spaceship is pretty unique. I also really liked the movement in the background and how it feels a bit circular.
The UI is a little bit complicated, and I had to double check which buttons did what in order to really get it. Perhaps some icons in game would help alleviate that. Also, I wasn't sure what the point of upgrading things like my oxygen and railgun were, maybe that could be explained better with a tooltip of some kind?
The sound was also a bit heavy attack heavy, it's quite jarring to hear such a strong sound every time anything happens in the game. I would mellow out some of the more common sounds and save the heavy ones for important things (like dying, etc...)
Overall, a fun game and nice interpretation of a classic genre. Great work! :)