This game is insane. I will probably never beat it but even attempting the first 2 levels over and over again has been more fun than you'd expect.
It's a bullet hell (meaning there is a ton of bullets on screen and you're expected to dodge them all) but mixed with a polarity-swapping technique. Enemies are of 2 colors, and you have the ability to be 1 of the 2 colors at a time. You absorb bullets of the same polarity and die to bullets of the opposite. You shoot the same color as your polarity, and shooting enemies with matching polarity does double damage. Shooting the correct polarity across multiple enemies rewards you with a chain, which leads to a higher score (which is the point of this game).
It's one of the hardest games I've played, and this is supposedly not even nearly as hard as other games in the genre. If you like a challenge you will certainly find it in this game. I don't think anyone with any amount of gaming experience can just pick up this game and get to level 5 even within a few days. It takes lots of practice and memorization and on top of all that perfect execution to proceed through the entirety of the game.
The level design is basically art. It's amazing how they've used the polarity technique to actually generate level obstacles that, in tandem with the spawning enemies, create an entire level that you're expected to dodge and blow up while maintaining a combo and getting the highest score possible. You can tell a lot of work went into the precise timings and enemy types of enemy spawns. The bosses are very unique and well designed as well. You almost never feel like they've repeated anything in the game. Every 5 seconds you're facing something new.
This game is easily a 9/10, more or less depending on your individual taste for bullet hells.