Good for casual fun
This game is fairly entertaining and good if you want to blow something up while listening to your music. It is really addicting in the beginning, because you'll be playing songs to unlock weapons for your ship and getting points to upgrade them. I really like that you can rotate the weapons around to make them shoot at different angles in the ship customization. The game is pretty easy, since you have infinite lives; so you can't fail. Each death however, does reduce your score and thus earn you less points.
However the game does come with many flaws. The first annoyance is that there is no search feature for songs, like in Osu! So if you have a large library of songs, you can't use a search function to find the song you want to play. There is a filter system, but it's not optimal at all.
As for actual gameplay, some of the design choices will annoy you, your ship has an amazingly large hitbox and you barely have space to actually manoeuvre around. Enemies will spawn in front and at the side, so sometimes you will have absolutely no room to move at all. Some of the hits can one shot you. There are so many flashy particles on screen that you sometimes can't see the enemies or bullets coming.
Dying is one of the worst feeling ever, not because you lose points, but it feels like an eternity. When you die, you want to jump back right in, but instead you have to wait for quite some while before you respawn. When you respawn, you don't clear the screen of enemies, so if there are a lot of enemies left on screen, you'll end up dying again.
As you progress further into the game, it only goes downhill from there. At higher difficulty, more enemies spawn with higher hitpoints, making it frustrating to move around and survive. It does give you more points, but by the time you unlock the final difficulty, you would already have unlocked the normal weapons and upgrades you want. The only motivation for you to play the songs after 7 hours of playtime is to either hope for a rare weapon (which is just a more powerful version of the normal weapons you can unlock) or to progress the 'story' of the game.
Overal I did had some fun with the game, but it comes with many annoyances. If you don't have a lot of music or don't like to listen to music, I wouldn't recommend the game; you need over 100 songs at least to fully enjoy the game. Also if you a hardcore Shoot 'Em Up player (like TouHou), you probably won't enjoy this game either. The game isn't 'challenging', but it is fun to shoot at stuff and get better weapons.
I rate this game 63 out of 100 points.