Truly incredible rhythm game. The concept is easy and graspable enough to appeal to casuals, but has a learning curve steep enough to tempt players to get better. The ability to unlock secrets with higher grades to compel continued playing was a really nice feature as well. It even drove me to get a perfect S Rank on all the songs (Yes, that includes the bonuses. Don't even get me started on how long those took me xD).
Speaking of songs, the quality of the music in this game is incredible, with unique beats and catchy tunes. Intimate is one of the best tracks I've heard in a long while; very well paced, and just beautiful. And, oh, the boss. The intended glitches in the track adds another depth to the rhythmic and sound-based capabilities of the song; simply amazing.
The difficulty is very well balanced, with early levels being just easy enough and the later bonuses really taking a few tries to master. It's as difficulty ramp-up should be.
I can personally tell a lot of love was put into this game. Free of glitches, and with the nice little additions like the disco colors changing only on each beat of the heart. Every nook and cranny of this game is very well polished.
Overall, an excellent edition to the rhythm game genre. I hope this game receives as much praise and support as it deserves; my condolences go out to the devs of the game. Great job. May you hold much success with this game in the future.