Personally the rhythm minigame is my least favorite part of this game. The given songs have this very calm style but at the same time they give you a lot of notes, which makes it feel badly mapped, simply because they are songs that don't work for a rhythm minigame, however I recommend this DLC because I recognize that *I* am not a big fan of rhythm games and when I play them, they are not usually songs like this. I don't feel it's a bad DLC, but somewhat completely unnecessary if you're not interested in playing a 2key, as this dlc has no achievements.

The rewards for doing all the songs and having the maximum score/getting to first place in the leaderboards are nothing more than visual things, not buffs or anything that affect the gameplay (and I say this as a good thing). Going into detail; you get 1 CG of the goddess, a little bit of dialogue (1-2min) with this character that I'll reveal in a separate spoiler and an outfit with glasses and dark clothing. The goddess of music is Okina Matara, from Touhou 16 ~ Hidden Star in Four Seasons. It's nice to be able to see her ingame, but sadly it's for very little time beyond the CG that you can always check out.

Conclusion; DLC 2.5 is more of an "extra" sold on the side. There are no achievements and the only incentive to buy it if you're not interested in the rhythm minigame/songs is just the visual stuff I detailed in the spoiler above.