Disclaimer: I fully understand this is a game jam game not everything can be done but even then I give very "tough" feedback so if you can't handle that kind of "criticism" it's ok just don't read my message.
First off consistency is key, do not combine fonts like arial and pixel art assets, either use fonts like arial with vector assets or use pixel fonts with pixel art assets, same with the UI as the button for start for example is quite blurry on the edges and the other 2 menu options don't even have a button UI and atleast in my experience the O in info overlapped with credits. When using placeholder/premade assets make sure the styles go well together.
Do not just use solid colors as backgrounds especially for these type of games, doing a tileset for the "ground" with even slight terrain alterations and basic decoration can go a long way if done right.
It's really unfortunate to hear no music nor any sfx, there's also lack of visual feedback in shooting, hitting "enemies" and that. This type of game also benefits quite a lot from enemy variety so if you plan on putting time onto this take that into account.
All in all, that's all I can say for now, hey, you managed to submit and publish, that's already good enough and wish you good luck for the future.