It's fun, it can definitely use some more polishing though. Sometimes it feels unresponsive or not responsive enough, it lacks of basic modern rhythm game options such as custom maps, skins (or any type of mod loader in general), multiplayer and remaps for the keys. These types of games must be played with keys on a horizontal line because the way they're layed out on a normal keyboard makes it uncomfortable to play at times.

A lot of people love the presentation but I honestly hesitated to try it for that motive, I think the "quirky simplistic" artstyle has already died down for me.
Honestly, it's free, you can try it out and it's fun. I just hope it gets some more basic features because the week system gets old quickly. A multiplayer mode could really benefit from the "duel" type of rhythm game in which both sides are displayed.