Firstly: most people (including me) don't like it when a jam game has to be installed. Just share it as a zip.
The artwork was stunning, but unfortunately there's a lot more to good visuals than just artwork. For starters, there's graphic design and game juice, which your game lacked a lot of: particle effects, screenshake, additional VFX like smoke or clouds, shaders, and then nice-looking and sleek menus, transitions, proper win screens, etc.
As for fun, I have to say that the gameplay was lackluster; running around and just shooting normally seemed to do the trick just fine. There's a great video on how to double the fun of a game in no time.
I just saw that this was your first game. Try not to be discouraged, but learn from your mistakes. I almost always only point out the flaws not because the game is necessarily bad, just because you don't really learn much from your successes.