What the heck this is freaking amazing! Its like Smash TV but with a great cute premise and the shooting and response is excellent.
Its got a deep upgrade and continue structure involving investing in card upgrades and matching them up with a clever memory game that makes the upgrade system itself fun and strategic which means in a given run there is chance but also substantial strategy to the upgrades you choose to get but also you can always grind and save up to invest in a run this makes it never feel unfair.
The crystals system also makes each run feel positive even if you don't get very far since it is always progress. But you can also gamble on a run and invest in it and then theres more pressure if you lose but it was completely up to you. The game never takes from you unfairly and that is a huge factor to how much fun this is as an experience. Its a rewarding and excellent system that more games should adopt something similar anyway.
The feel of just scooting around and turning with the right stick is crisp and satisfying to do. I think one of the excellent details is how they did the sprite aim rotation. It is beautiful and clever and fools the eyes.
There is a cool story to get you into what you are doing here and to make you want to take down the bosses, but also exploring this place is fun in and of itself. I started at 9pm and at 1am I was still playing and would have literally run it again right then if I hadn't needed sleep so bad.
Add into all of this: its got co op too! It is better than Smash TV tbh because of its much more fair difficulty curve and more interesting enemies.
For modifiers you can play with limitations such as only using crystals you picked up on this run or without using any crystals at all, or using powerups in a particular order (see Dave the Knave's strategy guide in the comment below) or switching playable characters since they play (shoot) totally different, or you can change control schemes to keyboard and mouse.
P.S. the soundtrack is great too. Its clear they had legit great musicians composing and recording this and it never got old. Anyway this is a masterpiece. Thank you!