I played through and beat the main story of this game in about 2.5 hours. I don't really feel drawn to replay it or climb leaderboards.
Overall, it's kinda fun, but it's just not fun enough to recommend (compared to the plethora of other, more fun games you could be playing).
As a shooter/SHMUP, it just feels weak. This feeling of weakness comes from everything from the music and sound to the gameplay mechanics and art.
Your gun and the enemy guns shoot tiny bullets that just go "pew pew". You can't spam your shots either - you have limited ammo with each ship so you'll find the gameplay consisting of making tiny adjustments, trying to line up with an enemy ship, and tapping once only to hear a pathetic "pew" and weak "retro" explosion sound effect. The hitboxes don't match up with the enemy sprites at all - the actual hitbox for an enemy is usually smaller than the actual sprite, which makes it even more frustrating to try to line up shots.
The music is just as tinny and weak sounding as the sound effects. It's actually fine that it blends in with the whole soundscape of the game, but overall I just found it to be entirely forgettable and not add to the game at all.
Furthermore, and this is probably the most detrimental to the core gameplay: the art lacks hard edges/contrast and makes it difficult to tell what is going on. When there's a lot of stuff on the screen, it becomes a huge cluster of nonsense and makes it very difficult to parse the game state and keep track of yourself. A simple addition of a few visual cues, some nice hard outlines for the enemies or something like that would've done loads to enable more satisfying, skillful play. They did a great job of making the enemy types easy to distinguish so I'm surprised that the devs didn't consider this sort of issue.
There's also several other frustrating bits. Things like the enemies being able to turn around when they get behind you and shoot you. It's just not very fun to deal with.
At times, however, this game does manage to be quite fun when you're successfully stringing together several jumps and taking out lots of enemies as you go. These moments are few and far between, but I imagine if you played it more and got more skillful you would experience this more often. Also, the challenging parts of this game are quite rewarding when you finally beat them. They also avoided making it too frustrating by letting you continue from the wave you were on even when you lose all of your lives (though your score is reset).
The story is quite cryptic and so sparsely told throughout the game that I had a hard time following it.
In conclusion, just contrast this with the feel of playing something like Raiden where you're making tiny corrections to dodge through swarms of bullets, all the while firing away with an upgradeable massive weapon, wreaking havoc on the enemy and causing explosions everywhere while a rad soundtrack plays. That's partially one of the things that makes those games fun to play - the amount of polish that went into evoking a feeling of power and intensity. This game just doesn't evoke that feeling, and maybe it didn't intend to, but it just doesn't FEEL fun.
If you're just looking for something new and like climbing leaderboards and raising your high score, you might enjoy this, but why not play a more thrilling game?