It is very fun, however, it's still a short prototype.

Personally, this game has two things I'm not a fan of. The CRT shader and shapes.

I get it it's a prototype, but eventually nobody wants to play as a triangle, and I'd argue there are a handful of games that got successful only with shapes. You need to give the game personality, maybe some basic pixel art ships will be enough, other than that it won't be a memorable experience. I've played dozens of games made with basic shapes, and I can't remember the name of any of them, except for geometry dash I guess, while I do remember a lot of indie game titles because their themes were memorable.

The CRT shader is just a personal opinion, I get why people use it, but in general devs just slap it in to "make it look retro" when the theme is not even retro, it's a lazy way to make your game look better or more interesting than what it actually is. I don't think this is the case here, if you remove the shader the game will still look good, but every time I see a CRT shader I'm like "seriously? again?". Still, if you could add an option to disable it, it would be nice.

About the gameplay, it's fun, and engaging, but I found that the "exclusive hovering" actually has some problems. First of all, I don't see a reason why the triangle (ship?) can't fire automatically. Or at least have an upgrade to allow it. The only thing hovering does is to force you to keep the mouse in the middle of the screen since there's no aiming or anything. Also, the fact that I have to stop firing to go to the upgrades, hold the mouse there for a few milliseconds and then come back made me lose a couple of rounds, mainly when enemies were very close and I needed a rate upgrade that could have probably saved me, so even if the theme is to make a game about hovering, I'm not sure if the gameplay is properly solved since it doesn't even pause the game, you have to leave the ship/triangle unattended while enemies are still coming and attacking and damaging you. There's something not right about it.

Still, the game is super fun, it probably needs those things polished about the gameplay, add more levels and enemies and it could be a hit.

Hope it helps! Good luck!