For a proof of concept, this has pretty good visuals and a lot of content. I was expecting something a lot more barebones when I saw that label. The music feels placeholder-y, but that might just be because these are the tracks I use as placeholder music in my own projects.
The mechanics... I have mixed feelings, but I'm also terrible at bullet hells. The bullet hell/shmup part seems well implementd, though I'm not a fan of the bullet sponge bosses. It's more the blending I'm skeptical of. All the cards I was dealt didn't seem all that useful, and it wasn't clear what some of them actually did. I think it could work. I think if the cards were buffed a bit and had more dramatic effects, they would work better.
I wasn't able to beat any of the bosses, but I found the first one- Rhyn- was actually the hardest. The combination of moving background and "motion blur" made it very hard to aim or even look at.
I didn't really pay attention to the narrative, to be honest. It's delivered awkwardly, in a tiny dialogue box and when I'm busy selecting cards.
I did run into glitches where the game stopped responding to input but I was also playing the web version, which I know is not recommended.