Wow, very cool game! All around very impressive craftmanship in all aspects and a great, fun concept: always enjoy seeing these one button games and I found this very addictive to get good at balancing attacking and movement since they all come from the same action and create some frantic fun. I felt like some aspects were a little unneeded, like weapon drops and cards as the game already felt great without them, but they were an alright addition for people who want a bit of RNG to help replayability, so I understand.
I definitely did have a bit of a rough start though: it was intuitive for the most part, but I didn't like how the game didn't have a 'how to play' as some aspects like the filling up of the blood gauge being how you make the exit portal was unclear. I also got tricked into thinking that charge up shots were the way to go since the game seemed to put emphasis on that, combined with the fact that uncharged shots were so weak: that led to me only relying on charged shots which was a frustrating period of getting screwed over while waiting for a charge up and not realizing that you can still move fast by mashing rapid fire weak shots.
I also hated some aspects of the gameplay such as the random spawns which can screw you over, the camera being too zoomed in which, when combined with the large distance you can travel, means you can constantly screw yourself over by zooming into unknown space, and the fact that the timer doesn't stop when you're in that intermission period between levels where you pick the next difficulty, meaning you're forced to just fire at whatever is closest and not knowing what you picked.